Investments - SLP Schedule of Investments (Details) € in Thousands, £ in Thousands, kr in Thousands, kr in Thousands, $ in Thousands, $ in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2022 AUD ($)	Sep. 30, 2022 EUR (€)	Sep. 30, 2022 GBP (£)	Sep. 30, 2022 CAD ($)	Dec. 31, 2021 AUD ($)	Dec. 31, 2021 EUR (€)	Dec. 31, 2021 GBP (£)	Dec. 31, 2021 CAD ($)	Dec. 31, 2021 DKK (kr)	Dec. 31, 2021 NOK (kr)
Investments
Investments, amortized cost	$ 2,356,143	$ 2,311,384
Investments at fair value	$ 2,293,522	$ 2,289,105
Investment, Identifier [Axis]: 9 Story Media Group Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Nine Story Media Group Inc [Member]	Nine Story Media Group Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Identifier [Axis]: 9 Story Media Group Inc. First Lien Senior Secured Loan Cdor
Investments
Spread Above Index (as a percent)	5.25%	5.50%	5.25%	5.25%	5.25%	5.25%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.03%	6.25%	9.03%	9.03%	9.03%	9.03%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares						$ 1,295				$ 72
Investments, amortized cost	$ 1,004									54
Investments at fair value	$ 937									$ 57
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Nine Story Media Group Inc [Member]	Nine Story Media Group Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: 9 Story Media Group Inc. First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate	5.83%	5.25%	5.83%	5.83%	5.83%	5.83%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Maturity date	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares | €				€ 586				€ 39
Investments, amortized cost	$ 621							45
Investments at fair value	$ 573							€ 44
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Nine Story Media Group Inc [Member]	Nine Story Media Group Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: A&R Logistics, Inc First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	8.35%	7.00%	8.35%	8.35%	8.35%	8.35%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 2,066	$ 2,815
Investments, amortized cost	1,954	2,748
Investments at fair value	$ 2,066	$ 2,815
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: A&R Logistics, Inc First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	8.23%	7.00%	8.23%	8.23%	8.23%	8.23%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 5,928	$ 43,092
Investments, amortized cost	5,881	42,527
Investments at fair value	$ 5,928	$ 43,092
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: A&R Logistics, Inc First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	8.23%	7.00%	8.23%	8.23%	8.23%	8.23%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 2,405	$ 2,423
Investments, amortized cost	2,379	2,391
Investments at fair value	$ 2,405	$ 2,423
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: A&R Logistics, Inc First Lien Senior Secured Loan 3
Investments
Spread Above Index (as a percent)	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	9.71%	7.00%	9.71%	9.71%	9.71%	9.71%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 32,064	$ 5,974
Investments, amortized cost	31,731	5,916
Investments at fair value	$ 32,064	$ 5,974
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: A&R Logistics, Inc First Lien Senior Secured Loan 4
Investments
Spread Above Index (as a percent)	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate	8.73%	7.50%	8.73%	8.73%	8.73%	8.73%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 2,695	$ 2,716
Investments, amortized cost	2,679	2,695
Investments at fair value	$ 2,695	$ 2,716
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: A&R Logistics, Inc First Lien Senior Secured Loan 5
Investments
Spread Above Index (as a percent)	6.60%		6.60%	6.60%	6.60%	6.60%
Interest rate	9.23%		9.23%	9.23%	9.23%	9.23%
Maturity date	May 05, 2025		May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 1,319
Investments, amortized cost	1,306
Investments at fair value	$ 1,319
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: ACAMS Equity Interest
Investments
Principal/Shares	$ 3,337
Investments, amortized cost	3,337
Investments at fair value	$ 3,309
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ACAMSMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: ACM dcBLOX LLC Preferred Equity
Investments
Principal/Shares		$ 3,822
Investments, amortized cost		3,851
Investments at fair value		$ 4,130
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ACMdcBLOXLLCMember
Investment, Type [Extensible Enumeration]		Preferred Stock [Member]					Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Identifier [Axis]: ADT Pizza, LLC Equity Interest
Investments
Principal/Shares	$ 6,720	$ 6,720
Investments, amortized cost	6,720	6,720
Investments at fair value	$ 14,581	$ 19,527
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ADTPizzaLLCMember	bcsf:ADTPizzaLLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Equity Securities [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]	Beverage Food And Tobacco Sector Non-controlled Affiliate Investments [Member]
Investment, Identifier [Axis]: AMCP Clean Acquisition Company, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.25%		4.25%	4.25%	4.25%	4.25%
Interest rate	7.37%		7.37%	7.37%	7.37%	7.37%
Maturity date	Jul. 10, 2025		Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025
Principal/Shares	$ 16,297
Investments, amortized cost	16,174
Investments at fair value	$ 13,222
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AMCPCleanAcquisitionCompanyLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: AMCP Clean Acquisition Company, LLC First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	4.25%		4.25%	4.25%	4.25%	4.25%
Interest rate	7.37%		7.37%	7.37%	7.37%	7.37%
Maturity date	Jul. 10, 2025		Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025
Principal/Shares	$ 3,944
Investments, amortized cost	3,914
Investments at fair value	$ 3,198
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AMCPCleanAcquisitionCompanyLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: AMCP Clean Acquisition Company, LLC First Lien Senior Secured Loan - Delayed Draw Libor
Investments
Spread Above Index (as a percent)		4.25%					4.25%	4.25%	4.25%	4.25%	4.25%	4.25%
Interest rate		4.35%					4.35%	4.35%	4.35%	4.35%	4.35%	4.35%
Maturity date		Jul. 10, 2025					Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025
Principal/Shares		$ 3,816
Investments, amortized cost		3,810
Investments at fair value		$ 3,189
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:AMCPCleanAcquisitionCompanyLLCMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: AMCP Clean Acquisition Company, LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		4.25%					4.25%	4.25%	4.25%	4.25%	4.25%	4.25%
Interest rate		4.35%					4.35%	4.35%	4.35%	4.35%	4.35%	4.35%
Maturity date		Jul. 10, 2025					Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025	Jul. 10, 2025
Principal/Shares		$ 15,767
Investments, amortized cost		15,747
Investments at fair value		$ 13,176
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:AMCPCleanAcquisitionCompanyLLCMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: AMI US Holdings Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.25%	5.50%	5.25%	5.25%	5.25%	5.25%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	7.81%	6.50%	7.81%	7.81%	7.81%	7.81%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025
Principal/Shares	$ 3,866	$ 12,892
Investments, amortized cost	3,830	12,735
Investments at fair value	$ 3,866	$ 12,892
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AMIUSHoldingsIncMember	bcsf:AMIUSHoldingsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: AMI US Holdings Inc. First Lien Senior Secured Loan - Revolver Libor
Investments
Spread Above Index (as a percent)		5.25%					5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate		5.35%					5.35%	5.35%	5.35%	5.35%	5.35%	5.35%
Maturity date		Apr. 01, 2024					Apr. 01, 2024	Apr. 01, 2024	Apr. 01, 2024	Apr. 01, 2024	Apr. 01, 2024	Apr. 01, 2024
Principal/Shares		$ 698
Investments, amortized cost		682
Investments at fair value		$ 698
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:AMIUSHoldingsIncMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: AQ Software Corporation Preferred Equity
Investments
Principal/Shares	$ 1	$ 1
Investments, amortized cost	1,107	1,029
Investments at fair value	$ 1,104	$ 1,029
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AQSoftwareCorporationMember	bcsf:AQSoftwareCorporationMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: AQ Software Corporation Preferred Equity 1
Investments
Principal/Shares	$ 2	$ 2
Investments, amortized cost	1,844	1,715
Investments at fair value	$ 1,839	$ 1,715
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AQSoftwareCorporationMember	bcsf:AQSoftwareCorporationMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: AQ Software Corporation Preferred Equity 2
Investments
Principal/Shares	$ 1
Investments, amortized cost	507
Investments at fair value	$ 506
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AQSoftwareCorporationMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: ARL Holdings, LLC Equity Interest
Investments
Principal/Shares		$ 445
Investments, amortized cost		445
Investments at fair value		$ 575
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ARLHoldingsLLCMember
Investment, Type [Extensible Enumeration]		Common Stock [Member]					Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Cargo [Member]					Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: ARL Holdings, LLC Equity Interest 1
Investments
Principal/Shares	$ 0	$ 9
Investments, amortized cost	445	9
Investments at fair value	$ 619	$ 81
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLHoldingsLLCMember	bcsf:ARLHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: ARL Holdings, LLC Equity Interest 2
Investments
Principal/Shares	$ 9
Investments, amortized cost	9
Investments at fair value	$ 334
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: ASP-r-pac Acquisition Co LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Dec. 29, 2027					Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027
Principal/Shares		$ 27,339
Investments, amortized cost		26,793
Investments at fair value		$ 26,792
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ASP-r-pacAcquisitionCoLLCMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Containers Packaging And Glass [Member]					Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: ASP-r-pac Acquisition Co LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027
Principal/Shares		$ 651
Investments, amortized cost		586
Investments at fair value	$ (24)	$ 586
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ASP-r-pacAcquisitionCoLLCMember	bcsf:ASP-r-pacAcquisitionCoLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: ASP-r-pac Acquisition Co LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	Dec. 29, 2027		Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027
Principal/Shares	$ 4,093
Investments, amortized cost	4,041
Investments at fair value	$ 4,063
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ASP-r-pacAcquisitionCoLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Containers Packaging And Glass [Member]		Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Abracon Group Holding, LLC Equity Interest
Investments
Principal/Shares		$ 2
Investments, amortized cost		1,833
Investments at fair value		$ 3,282
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:AbraconGroupHoldingLLCMember
Investment, Type [Extensible Enumeration]		Equity Securities [Member]					Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]		Wholesale					Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Identifier [Axis]: Abracon Group Holding, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%	5.25%	6.00%	6.00%	6.00%	6.00%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate	7.86%	6.25%	7.86%	7.86%	7.86%	7.86%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date	Jul. 06, 2028	Jul. 18, 2024	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024
Principal/Shares	$ 11,547	$ 35,363
Investments, amortized cost	11,322	35,270
Investments at fair value	$ 11,315	$ 35,363
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AbraconGroupHoldingLLCMember	bcsf:AbraconGroupHoldingLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Abracon Group Holding, LLC First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Jul. 06, 2028	Jul. 18, 2024	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024	Jul. 18, 2024
Investments at fair value	$ (40)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AbraconGroupHoldingLLCMember	bcsf:AbraconGroupHoldingLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Identifier [Axis]: Abracon Group Holding, LLC. First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Jul. 06, 2028		Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028
Investments at fair value	$ (50)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AbraconGroupHoldingLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Wholesale		Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Access First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	5.75%		5.75%	5.75%	5.75%	5.75%
Maturity date	Jun. 02, 2029		Jun. 02, 2029	Jun. 02, 2029	Jun. 02, 2029	Jun. 02, 2029
Principal/Shares | £					£ 3,217
Investments, amortized cost	$ 3,318
Investments at fair value	$ 3,483
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Access [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Access First Lien Senior Secured Loan Sonia
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	7.44%		7.44%	7.44%	7.44%	7.44%
Maturity date	Jun. 02, 2029		Jun. 02, 2029	Jun. 02, 2029	Jun. 02, 2029	Jun. 02, 2029
Principal/Shares | £					£ 7,960
Investments, amortized cost	$ 9,770
Investments at fair value	$ 8,801
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Access [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Aimbridge Acquisition Co., Inc. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.50%		7.50%	7.50%	7.50%	7.50%
Interest rate	10.06%		10.06%	10.06%	10.06%	10.06%
Maturity date	Feb. 01, 2027		Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027
Principal/Shares	$ 14,193
Investments, amortized cost	13,906
Investments at fair value	$ 13,413
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AimbridgeAcquisitionCoIncMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Aimbridge Acquisition Co., Inc. Second Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Interest rate		7.59%					7.59%	7.59%	7.59%	7.59%	7.59%	7.59%
Maturity date		Feb. 01, 2027					Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027
Principal/Shares		$ 20,193
Investments, amortized cost		19,772
Investments at fair value		$ 18,679
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:AimbridgeAcquisitionCoIncMember
Investment, Type [Extensible Enumeration]		Second Lien Senior Secured Loan [Member]					Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Hotel, Gaming & Leisure					Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%	5.00%	4.75%	4.75%	4.75%	4.75%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate	7.88%	6.00%	7.88%	7.88%	7.88%	7.88%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Principal/Shares	$ 1,509	$ 10,037
Investments, amortized cost	1,493	9,908
Investments at fair value	$ 1,509	$ 10,037
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AllworthFinancialGroupLPMember	bcsf:AllworthFinancialGroupLPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	4.75%	5.00%	4.75%	4.75%	4.75%	4.75%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate	7.88%	6.00%	7.88%	7.88%	7.88%	7.88%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Principal/Shares	$ 876	$ 2,528
Investments, amortized cost	863	2,476
Investments at fair value	$ 876	$ 2,528
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AllworthFinancialGroupLPMember	bcsf:AllworthFinancialGroupLPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AllworthFinancialGroupLPMember	bcsf:AllworthFinancialGroupLPMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Identifier [Axis]: American Trailer Rental Group Subordinated Debt
Investments
Spread Above Index (as a percent)	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%
Maturity date	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027
Principal/Shares	$ 4,973	$ 4,913
Investments, amortized cost	4,909	4,842
Investments at fair value	$ 4,973	$ 4,913
PIK	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AmericanTrailerRentalGroupMember	bcsf:AmericanTrailerRentalGroupMember
Investment, Type [Extensible Enumeration]	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: American Trailer Rental Group Subordinated Debt 2
Investments
Spread Above Index (as a percent)	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%	11.00%
Maturity date	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027
Principal/Shares	$ 15,344	$ 15,114
Investments, amortized cost	15,053	14,793
Investments at fair value	$ 15,344	$ 15,114
PIK	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AmericanTrailerRentalGroupMember	bcsf:AmericanTrailerRentalGroupMember
Investment, Type [Extensible Enumeration]	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: American Trailer Rental Group Subordinated Debt 3
Investments
Spread Above Index (as a percent)	9.00%		9.00%	9.00%	9.00%	9.00%
Interest rate	11.00%		11.00%	11.00%	11.00%	11.00%
Maturity date	Dec. 01, 2027		Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027	Dec. 01, 2027
Principal/Shares	$ 19,161
Investments, amortized cost	18,772
Investments at fair value	$ 19,161
PIK	(2.00%)		(2.00%)	(2.00%)	(2.00%)	(2.00%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AmericanTrailerRentalGroupMember
Investment, Type [Extensible Enumeration]	Subordinated Debt		Subordinated Debt	Subordinated Debt	Subordinated Debt	Subordinated Debt
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]		Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Amspec Services, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%	6.75%	9.42%	9.42%	9.42%	9.42%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024
Principal/Shares	$ 2,784	$ 43,207
Investments, amortized cost	2,763	42,923
Investments at fair value	$ 2,784	$ 43,207
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Amspec Services Inc [Member]	Amspec Services Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Amspec Services, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Jul. 02, 2024					Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024
Principal/Shares		$ 1,488
Investments, amortized cost		1,457
Investments at fair value		$ 1,487
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Amspec Services Inc [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Energy Oil And Gas [Member]					Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Amspec Services, Inc. First Lien Senior Secured Loan - Revolver Prime Rate
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	10.00%		10.00%	10.00%	10.00%	10.00%
Maturity date	Jul. 02, 2024		Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024
Principal/Shares	$ 567
Investments, amortized cost	546
Investments at fair value	$ 567
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Amspec Services Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas [Member]		Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	us-gaap:PrimeRateMember		us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: Amspec Services, Inc. First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%	6.75%	9.42%	9.42%	9.42%	9.42%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024
Principal/Shares	$ 33,076	$ 2,798
Investments, amortized cost	32,922	2,768
Investments at fair value	$ 33,076	$ 2,798
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Amspec Services Inc [Member]	Amspec Services Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Ansett Aviation Training First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.69%		4.69%	4.69%	4.69%	4.69%
Interest rate	5.69%		5.69%	5.69%	5.69%	5.69%
Maturity date	Sep. 24, 2031		Sep. 24, 2031	Sep. 24, 2031	Sep. 24, 2031	Sep. 24, 2031
Principal/Shares			$ 7,072
Investments, amortized cost	$ 5,308
Investments at fair value	$ 4,525
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AnsettAviationTrainingMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:BankBillSwapBidRateMember		bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember
Investment, Identifier [Axis]: Ansett Aviation Training Equity Interest
Investments
Principal/Shares			$ 5,119
Investments, amortized cost			3,842
Investments at fair value			$ 3,277
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:AnsettAviationTrainingMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: Ansira Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Interest rate	9.31%		9.31%	9.31%	9.31%	9.31%
Maturity date	Dec. 20, 2024		Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024
Principal/Shares	$ 41,731
Investments, amortized cost	40,925
Investments at fair value	$ 20,866
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Ansira Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Advertising, Printing & Publishing		Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Ansira Holdings, Inc. First Lien Senior Secured Loan - Delayed Draw Libor
Investments
Spread Above Index (as a percent)	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate	9.57%	7.50%	9.57%	9.57%	9.57%	9.57%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024
Principal/Shares	$ 5,064	$ 4,873
Investments, amortized cost	5,066	4,874
Investments at fair value	$ 2,532	$ 3,862
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Ansira Holdings Inc [Member]	Ansira Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Ansira Holdings, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.79%		8.79%	8.79%	8.79%	8.79%
Maturity date	Dec. 20, 2024		Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024
Principal/Shares	$ 5,383
Investments, amortized cost	5,383
Investments at fair value	$ 1,842
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Ansira Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Media: Advertising, Printing & Publishing		Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Ansira Holdings, Inc. First Lien Senior Secured Loan - Revolver Prime
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		7.41%					7.41%	7.41%	7.41%	7.41%	7.41%	7.41%
Maturity date		Dec. 20, 2024					Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024
Principal/Shares		$ 5,383
Investments, amortized cost		5,383
Investments at fair value		$ 3,913
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Ansira Holdings Inc [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Media: Advertising, Printing & Publishing					Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]		us-gaap:PrimeRateMember					us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: Ansira Holdings, Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date		Dec. 20, 2024					Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024	Dec. 20, 2024
Principal/Shares		$ 40,086
Investments, amortized cost		40,057
Investments at fair value		$ 31,768
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Ansira Holdings Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Advertising, Printing & Publishing					Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Ap Plastic Group Llc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Interest rate	7.87%		7.87%	7.87%	7.87%	7.87%
Maturity date	Aug. 10, 2028		Aug. 10, 2028	Aug. 10, 2028	Aug. 10, 2028	Aug. 10, 2028
Principal/Shares	$ 7,306
Investments, amortized cost	7,087
Investments at fair value	$ 7,014
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ApPlasticsGroupLlcMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Chemicals, Plastics & Rubber		Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Apollo Intelligence Equity Interest
Investments
Principal/Shares	$ 32
Investments, amortized cost	3,162
Investments at fair value	$ 3,182
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Apollo Intelligence [Member]
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Identifier [Axis]: Apollo Intelligence First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.26%		8.26%	8.26%	8.26%	8.26%
Maturity date	Jun. 01, 2028		Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028
Principal/Shares	$ 15,425
Investments, amortized cost	15,277
Investments at fair value	$ 15,271
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Apollo Intelligence [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Apollo Intelligence First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Jun. 01, 2028		Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028
Investments at fair value	$ (96)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Apollo Intelligence [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Identifier [Axis]: Apollo Intelligence First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Jun. 01, 2028		Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028
Investments at fair value	$ (72)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Apollo Intelligence [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Identifier [Axis]: Applitools First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.30%		9.30%	9.30%	9.30%	9.30%
Maturity date	May 25, 2029		May 25, 2029	May 25, 2029	May 25, 2029	May 25, 2029
Principal/Shares	$ 24,696
Investments, amortized cost	24,460
Investments at fair value	$ 24,449
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Applitools [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Applitools First Lien Senior Secured Loan - Revolver
Investments
Maturity date	May 25, 2028		May 25, 2028	May 25, 2028	May 25, 2028	May 25, 2028
Investments at fair value	$ (34)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Applitools [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Appriss Holdings, Inc. Equity Interest
Investments
Principal/Shares	$ 2,136	$ 2,136
Investments, amortized cost	1,606	1,606
Investments at fair value	$ 1,505	$ 1,552
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Appriss Holdings Inc [Member]	Appriss Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	Common Stock [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Appriss Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		7.25%					7.25%	7.25%	7.25%	7.25%	7.25%	7.25%
Interest rate		8.25%					8.25%	8.25%	8.25%	8.25%	8.25%	8.25%
Maturity date		May 06, 2027					May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027
Principal/Shares		$ 11,292
Investments, amortized cost		11,081
Investments at fair value		$ 11,179
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Appriss Holdings Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Appriss Holdings, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027
Investments at fair value	$ (13)	$ (8)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Appriss Holdings Inc [Member]	Appriss Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Appriss Holdings, Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	7.25%		7.25%	7.25%	7.25%	7.25%
Interest rate	9.93%		9.93%	9.93%	9.93%	9.93%
Maturity date	May 06, 2027		May 06, 2027	May 06, 2027	May 06, 2027	May 06, 2027
Principal/Shares	$ 11,278
Investments, amortized cost	11,092
Investments at fair value	$ 11,081
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Appriss Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Aptus 1724 Gmbh First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.39%		9.39%	9.39%	9.39%	9.39%
Maturity date	Aug. 23, 2027		Aug. 23, 2027	Aug. 23, 2027	Aug. 23, 2027	Aug. 23, 2027
Principal/Shares	$ 4,971
Investments, amortized cost	4,971
Investments at fair value	$ 4,909
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Aptus1724GmbhMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Aptus 1724 Gmbh First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		Feb. 23, 2028					Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028
Principal/Shares | €								€ 4,162
Investments, amortized cost | €								5,055
Investments at fair value | €								€ 4,732
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Aptus1724GmbhMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Diversified & Production					Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:EuroInterbankOfferRateMember					bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Aptus 1724 Gmbh First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date		Feb. 23, 2028					Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028	Feb. 23, 2028
Principal/Shares		$ 14,971
Investments, amortized cost		14,971
Investments at fair value		$ 14,971
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Aptus1724GmbhMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Diversified & Production					Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Aramsco, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate	8.37%	5.35%	8.37%	8.37%	8.37%	8.37%	5.35%	5.35%	5.35%	5.35%	5.35%	5.35%
Maturity date	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024
Principal/Shares	$ 14,103	$ 23,796
Investments, amortized cost	13,979	23,537
Investments at fair value	$ 14,103	$ 23,796
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Aramsco Inc [Member]	Aramsco Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Aramsco, Inc First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.25%		5.25%	5.25%	5.25%	5.25%
Interest rate	8.37%		8.37%	8.37%	8.37%	8.37%
Maturity date	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024
Principal/Shares	$ 226
Investments, amortized cost	201
Investments at fair value	$ 226
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Aramsco Inc [Member]	Aramsco Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Armor Group, LP Equity Interest
Investments
Principal/Shares	$ 10	$ 10
Investments, amortized cost	1,012	1,012
Investments at fair value	$ 2,086	$ 2,131
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ArmorGroupLPMember	bcsf:ArmorGroupLPMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Equity Securities [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Identifier [Axis]: Armstrong Bidco Limited First Lien Senior Secured Loan Sonia
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Maturity date		Apr. 30, 2025					Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025
Principal/Shares		$ 56
Investments, amortized cost		78
Investments at fair value		$ 76
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ArmstrongBidcoLimitedMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]					Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Armstrong Bidco T/L First Lien Senior Secured Loan Sonia
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.06%					5.06%	5.06%	5.06%	5.06%	5.06%	5.06%
Maturity date		Apr. 30, 2025					Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025	Apr. 30, 2025
Principal/Shares | €								€ 705
Investments, amortized cost | €								763
Investments at fair value | €								€ 954
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Armstrong Bidco T/L
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]					Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Avalon Acquiror, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.80%		9.80%	9.80%	9.80%	9.80%
Maturity date	Mar. 10, 2028		Mar. 10, 2028	Mar. 10, 2028	Mar. 10, 2028	Mar. 10, 2028
Principal/Shares	$ 24,660
Investments, amortized cost	24,431
Investments at fair value	$ 24,229
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Avalon Acquiror, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Avalon Acquiror, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.38%		9.38%	9.38%	9.38%	9.38%
Maturity date	Mar. 10, 2028		Mar. 10, 2028	Mar. 10, 2028	Mar. 10, 2028	Mar. 10, 2028
Principal/Shares	$ 1,050
Investments, amortized cost	878
Investments at fair value	$ 903
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Avalon Acquiror, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: BCC Jetstream Holdings Aviation (Off I), LLC Equity Interest
Investments
Principal/Shares	$ 11,863	$ 11,863
Investments, amortized cost	11,863	11,863
Investments at fair value	$ 10,209	$ 10,563
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BCCJetstreamHoldingsAviationOnIILLCMember	bcsf:BCCJetstreamHoldingsAviationOffILLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: BCC Jetstream Holdings Aviation (On II), LLC Equity Interest
Investments
Principal/Shares	$ 1,116	$ 1,116
Investments, amortized cost	$ 1,116	$ 1,116
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BCCJetstreamHoldingsAviationOnIILLCMember	bcsf:BCCJetstreamHoldingsAviationOnIILLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: BCC Jetstream Holdings Aviation (On II), LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Interest rate	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date	Jun. 02, 2023	Jun. 02, 2022	Jun. 02, 2023	Jun. 02, 2023	Jun. 02, 2023	Jun. 02, 2023	Jun. 02, 2022	Jun. 02, 2022	Jun. 02, 2022	Jun. 02, 2022	Jun. 02, 2022	Jun. 02, 2022
Principal/Shares	$ 8,013	$ 7,377
Investments, amortized cost	8,013	7,377
Investments at fair value	$ 6,399	$ 6,627
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BCCJetstreamHoldingsAviationOnIILLCMember	bcsf:BCCJetstreamHoldingsAviationOnIILLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: BCC Middle Market CLO 2018-1, LLC Equity Interest
Investments
Maturity date	Oct. 20, 2030		Oct. 20, 2030	Oct. 20, 2030	Oct. 20, 2030	Oct. 20, 2030
Principal/Shares	$ 25,635
Investments, amortized cost	24,051
Investments at fair value	$ 22,298
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]		Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BCCMiddleMarketCLO2018-1LLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance Non Controlled Affiliate		Fire Finance Non Controlled Affiliate	Fire Finance Non Controlled Affiliate	Fire Finance Non Controlled Affiliate	Fire Finance Non Controlled Affiliate
Investment, Identifier [Axis]: Bain Capital Senior Loan Program, LLC Equity Interest Investment Vehicles
Investments
Principal/Shares	$ 5,594
Investments, amortized cost	5,594
Investments at fair value	$ 4,063
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]		Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	Bain Capital Senior Loan Program L L C [Member]
Investment, Type [Extensible Enumeration]	Equity Interest Investment Vehicles [Member]		Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]
Investment, Industry Sector [Extensible Enumeration]	Investment Vehicles [Member]		Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]
Investment, Identifier [Axis]: Bain Capital Senior Loan Program, LLC Preferred Equity Interest Investment Vehicles
Investments
Principal/Shares	$ 10
Investments, amortized cost	10
Investments at fair value	$ (433)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]		Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	Bain Capital Senior Loan Program L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:PreferredEquityInterestInvestmentVehiclesMember		bcsf:PreferredEquityInterestInvestmentVehiclesMember	bcsf:PreferredEquityInterestInvestmentVehiclesMember	bcsf:PreferredEquityInterestInvestmentVehiclesMember	bcsf:PreferredEquityInterestInvestmentVehiclesMember
Investment, Industry Sector [Extensible Enumeration]	Investment Vehicles [Member]		Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]
Investment, Identifier [Axis]: Bain Capital Senior Loan Program, LLC Subordinated Note Investment Vehicles
Investments
Spread Above Index (as a percent)	10.00%		10.00%	10.00%	10.00%	10.00%
Interest rate	10.00%		10.00%	10.00%	10.00%	10.00%
Maturity date	Dec. 27, 2033		Dec. 27, 2033	Dec. 27, 2033	Dec. 27, 2033	Dec. 27, 2033
Principal/Shares	$ 50,995
Investments, amortized cost	50,995
Investments at fair value	$ 50,995
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]		Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	Bain Capital Senior Loan Program L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:SubordinatedNoteInvestmentVehiclesMember		bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember
Investment, Industry Sector [Extensible Enumeration]	Investment Vehicles [Member]		Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]
Investment, Identifier [Axis]: Batteries Plus Holding Corporation First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.75%		6.75%	6.75%	6.75%	6.75%
Interest rate	9.87%		9.87%	9.87%	9.87%	9.87%
Maturity date	Jun. 30, 2023		Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023
Principal/Shares	$ 18,172
Investments, amortized cost	18,172
Investments at fair value	$ 18,172
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Batteries Plus Holding Corporation [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Batteries Plus Holding Corporation First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	12.00%		12.00%	12.00%	12.00%	12.00%
Maturity date	Jun. 30, 2023		Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023
Principal/Shares	$ 2,038
Investments, amortized cost	2,037
Investments at fair value	$ 2,038
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Batteries Plus Holding Corporation [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	us-gaap:PrimeRateMember		us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: Batteries Plus Holding Corporation First Lien Senior Secured Loan - Revolver Prime
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		8.44%					8.44%	8.44%	8.44%	8.44%	8.44%	8.44%
Maturity date		Jun. 30, 2023					Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023
Principal/Shares		$ 817
Investments, amortized cost		817
Investments at fair value		$ 817
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Batteries Plus Holding Corporation [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		us-gaap:PrimeRateMember					us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: Batteries Plus Holding Corporation First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Interest rate		7.75%					7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Maturity date		Jun. 30, 2023					Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023
Principal/Shares		$ 28,672
Investments, amortized cost		28,671
Investments at fair value		$ 28,671
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Batteries Plus Holding Corporation [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Blackbrush Oil & Gas, L.P. Equity Interest
Investments
Principal/Shares	$ 1,198	$ 1,123
Investments, amortized cost	$ 1
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BlackbrushOilGasLPMember	bcsf:BlackbrushOilGasLPMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Equity Securities [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Blackbrush Oil & Gas, L.P. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate	9.11%	8.00%	9.11%	9.11%	9.11%	9.11%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%
Maturity date	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025
Principal/Shares	$ 8,995	$ 12,336
Investments, amortized cost	8,993	12,336
Investments at fair value	$ 8,995	$ 12,336
PIK	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)	(2.00%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BlackbrushOilGasLPMember	bcsf:BlackbrushOilGasLPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Blackbrush Oil & Gas, L.P. Preferred Equity
Investments
Principal/Shares	$ 38,505	$ 36,084
Investments, amortized cost	11,777	10,104
Investments at fair value	$ 29,476	$ 19,720
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BlackbrushOilGasLPMember	bcsf:BlackbrushOilGasLPMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]	Energy Oil And Gas Noncontrolled Affiliate Investments [Member]
Investment, Identifier [Axis]: Brook Bidco Facility B First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.09%					6.09%	6.09%	6.09%	6.09%	6.09%	6.09%
Maturity date		Jul. 07, 2028					Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028
Principal/Shares | £									£ 684
Investments, amortized cost | £									935
Investments at fair value | £									£ 926
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:BrookBidcoFacilityBMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Brook Bidco First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	3.00%		3.00%	3.00%	3.00%	3.00%
Interest rate	8.06%		8.06%	8.06%	8.06%	8.06%
Maturity date	Jul. 07, 2028		Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028
Principal/Shares | £					£ 707
Investments, amortized cost	$ 964
Investments at fair value	$ 789
PIK	(4.25%)		(4.25%)	(4.25%)	(4.25%)	(4.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BrookBidcoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Brook Bidco I Limited First Lien Senior Secured Loan - Revolver Gbp libor 1
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Jul. 07, 2028					Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028
Principal/Shares | £									£ 5,385
Investments, amortized cost | £									7,047
Investments at fair value | £									£ 7,287
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:BrookBidcoILimitedMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember					bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember
Investment, Identifier [Axis]: Brook Bidco I Limited First Lien Senior Secured Loan - Revolver Gbp libor 2
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Jul. 07, 2028					Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028
Principal/Shares | £									£ 7,180
Investments, amortized cost | £									9,396
Investments at fair value | £									£ 9,716
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:BrookBidcoILimitedMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember					bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember
Investment, Identifier [Axis]: Brook Bidco I Limited First Lien Senior Secured Loan, One
Investments
PIK	4.25%		4.25%	4.25%	4.25%	4.25%
Investment, Identifier [Axis]: Brook Bidco I Limited First Lien Senior Secured Loan, Three
Investments
PIK	4.25%		4.25%	4.25%	4.25%	4.25%
Investment, Identifier [Axis]: Brook Bidco I Limited First Lien Senior Secured Loan, Two
Investments
PIK	4.25%		4.25%	4.25%	4.25%	4.25%
Investment, Identifier [Axis]: Brook Bidco Preferred Equity
Investments
Principal/Shares | £					£ 5,675
Investments, amortized cost	$ 7,783
Investments at fair value	$ 7,028
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:BrookBidcoMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Brook Bidco Series A Preferred Units Preferred Equity
Investments
Principal/Shares		$ 5,675
Investments, amortized cost		7,783
Investments at fair value		$ 7,908
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:BrookBidcoSeriesAPreferredUnitsMember
Investment, Type [Extensible Enumeration]		Preferred Stock [Member]					Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: CB Nike IntermediateCo Ltd First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate	7.56%	5.75%	7.56%	7.56%	7.56%	7.56%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025
Principal/Shares	$ 344	$ 347
Investments, amortized cost	341	342
Investments at fair value	$ 344	$ 347
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	C B Nike Intermediate Co Ltd [Member]	C B Nike Intermediate Co Ltd [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: CB Nike IntermediateCo Ltd First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025
Principal/Shares		$ 44
Investments, amortized cost		44
Investments at fair value		$ 44
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	C B Nike Intermediate Co Ltd [Member]	C B Nike Intermediate Co Ltd [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: CB Titan Holdings, Inc. Preferred Equity
Investments
Principal/Shares	$ 1,953	$ 1,953
Investments, amortized cost	1,953	1,953
Investments at fair value	$ 918	$ 1,153
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:CBTitanHoldingsIncMember	bcsf:CBTitanHoldingsIncMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Identifier [Axis]: CPS Group Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.25%	5.75%	5.75%	5.75%	5.75%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate	9.42%	6.25%	9.42%	9.42%	9.42%	9.42%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025
Principal/Shares	$ 44,790	$ 54,843
Investments, amortized cost	44,582	54,517
Investments at fair value	$ 44,790	$ 54,843
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	C P S Group Holdings, Inc [Member]	C P S Group Holdings, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: CPS Group Holdings, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	C P S Group Holdings, Inc [Member]	C P S Group Holdings, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Identifier [Axis]: CST Buyer Company First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%	5.55%	5.50%	5.50%	5.50%	5.50%	5.55%	5.55%	5.55%	5.55%	5.55%	5.55%
Interest rate	8.62%	6.50%	8.62%	8.62%	8.62%	8.62%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025
Principal/Shares	$ 8,322	$ 19,238
Investments, amortized cost	8,294	19,122
Investments at fair value	$ 8,322	$ 19,238
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	C S T Buyer Company [Member]	C S T Buyer Company [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: CST Buyer Company First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:JHCCHoldingsLLCMember	C S T Buyer Company [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Identifier [Axis]: Captain Ds LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		4.50%					4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date		Dec. 15, 2023					Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023
Principal/Shares		$ 2,326
Investments, amortized cost		2,301
Investments at fair value		$ 2,326
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Captain D's LLC
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Hotel, Gaming & Leisure					Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Captain D’s LLC First Lien Senior Secured Loan - Revolver
Investments
Maturity date		Dec. 15, 2023					Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Captain D's LLC
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Hotel, Gaming & Leisure					Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Identifier [Axis]: Captain D’s LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		4.50%					4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date		Dec. 15, 2023					Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023	Dec. 15, 2023
Principal/Shares		$ 12,559
Investments, amortized cost		12,539
Investments at fair value		$ 12,559
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Captain D's LLC
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Hotel, Gaming & Leisure					Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Cardo First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%	6.00%	5.00%	5.00%	5.00%	5.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	7.09%	6.50%	7.09%	7.09%	7.09%	7.09%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028
Principal/Shares	$ 98	$ 10,898
Investments, amortized cost	97	10,795
Investments at fair value	$ 98	$ 10,898
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:CardoMember	bcsf:CardoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Caribou Bidco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	7.19%		7.19%	7.19%	7.19%	7.19%
Maturity date	Jan. 29, 2029		Jan. 29, 2029	Jan. 29, 2029	Jan. 29, 2029	Jan. 29, 2029
Principal/Shares | £					£ 8,070
Investments, amortized cost	$ 10,799
Investments at fair value	$ 9,014
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Caribou Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Caribou Bidco Limited First Lien Senior Secured Loan Not Qualifying
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	7.19%		7.19%	7.19%	7.19%	7.19%
Maturity date	Jan. 29, 2029		Jan. 29, 2029	Jan. 29, 2029	Jan. 29, 2029	Jan. 29, 2029
Principal/Shares | £					£ 16
Investments, amortized cost	$ 20
Investments at fair value	$ 18
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Caribou Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Chamber Bidco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	7.85%		7.85%	7.85%	7.85%	7.85%
Maturity date	Jun. 07, 2028		Jun. 07, 2028	Jun. 07, 2028	Jun. 07, 2028	Jun. 07, 2028
Principal/Shares	$ 237
Investments, amortized cost	235
Investments at fair value	$ 237
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ChamberBidcoLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Chamber Bidco Limited First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date		Jun. 07, 2028					Jun. 07, 2028	Jun. 07, 2028	Jun. 07, 2028	Jun. 07, 2028	Jun. 07, 2028	Jun. 07, 2028
Principal/Shares		$ 237
Investments, amortized cost		234
Investments at fair value		$ 237
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ChamberBidcoLimitedMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Chase Industries, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.00%	5.50%	7.00%	7.00%	7.00%	7.00%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.88%	6.50%	9.88%	9.88%	9.88%	9.88%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025
Principal/Shares	$ 13,828	$ 12,622
Investments, amortized cost	13,801	12,586
Investments at fair value	$ 11,063	$ 9,971
PIK	7.00%	(1.50%)	7.00%	7.00%	7.00%	7.00%	(1.50%)	(1.50%)	(1.50%)	(1.50%)	(1.50%)	(1.50%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ChaseIndustriesIncMember	bcsf:ChaseIndustriesIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Chase Industries, Inc.First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	7.00%	5.50%	7.00%	7.00%	7.00%	7.00%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.88%	6.50%	9.88%	9.88%	9.88%	9.88%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025	May 12, 2025
Principal/Shares	$ 1,307	$ 1,197
Investments, amortized cost	1,306	1,195
Investments at fair value	$ 1,046	$ 946
PIK	7.00%	(1.50%)	7.00%	7.00%	7.00%	7.00%	(1.50%)	(1.50%)	(1.50%)	(1.50%)	(1.50%)	(1.50%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ChaseIndustriesIncMember	bcsf:ChaseIndustriesIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: ClockSpring Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Interest rate	10.05%		10.05%	10.05%	10.05%	10.05%
Maturity date	Aug. 01, 2025		Aug. 01, 2025	Aug. 01, 2025	Aug. 01, 2025	Aug. 01, 2025
Principal/Shares	$ 5,235
Investments, amortized cost	5,145
Investments at fair value	$ 5,131
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ClockSpringMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Capital Equipment Sector [Member]		Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Concert Golf Partners Holdco First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	6.50%		6.50%	6.50%	6.50%	6.50%
Maturity date	Mar. 30, 2029		Mar. 30, 2029	Mar. 30, 2029	Mar. 30, 2029	Mar. 30, 2029
Principal/Shares	$ 6,847
Investments, amortized cost	6,724
Investments at fair value	$ 6,778
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ConcertGolfPartnersHoldcoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Concert Golf Partners Holdco LLC First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.40%		9.40%	9.40%	9.40%	9.40%
Maturity date	Mar. 30, 2029		Mar. 30, 2029	Mar. 30, 2029	Mar. 30, 2029	Mar. 30, 2029
Principal/Shares	$ 1,065
Investments, amortized cost	987
Investments at fair value	$ 1,023
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ConcertGolfPartnersHoldcoLlcMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Concert Golf Partners Holdco LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.46%		9.46%	9.46%	9.46%	9.46%
Maturity date	Mar. 31, 2028		Mar. 31, 2028	Mar. 31, 2028	Mar. 31, 2028	Mar. 31, 2028
Principal/Shares	$ 356
Investments, amortized cost	310
Investments at fair value	$ 331
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ConcertGolfPartnersHoldcoLlcMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Conterra Ultra Broadband Holdings, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date		Apr. 30, 2026					Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares		$ 6,321
Investments, amortized cost		6,300
Investments at fair value		$ 6,332
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ConterraUltraBroadbandHoldingsIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: DC Blox Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		8.00%					8.00%	8.00%	8.00%	8.00%	8.00%	8.00%
Interest rate		9.00%					9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Maturity date		Mar. 22, 2026					Mar. 22, 2026	Mar. 22, 2026	Mar. 22, 2026	Mar. 22, 2026	Mar. 22, 2026	Mar. 22, 2026
Principal/Shares		$ 16,998
Investments, amortized cost		16,738
Investments at fair value		$ 16,998
PIK		(6.00%)					(6.00%)	(6.00%)	(6.00%)	(6.00%)	(6.00%)	(6.00%)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:DCBloxIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: DC Blox Inc Warrants
Investments
Principal/Shares		$ 177
Investments, amortized cost		$ 2
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:DCBloxIncMember
Investment, Type [Extensible Enumeration]		Warrant [Member]					Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Identifier [Axis]: DC Blox Inc,Preferred Equity
Investments
Principal/Shares	$ 3,822
Investments, amortized cost	3,851
Investments at fair value	$ 4,449
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:DCBloxIncMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Identifier [Axis]: DC Blox Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	2.00%		2.00%	2.00%	2.00%	2.00%
Interest rate	11.29%		11.29%	11.29%	11.29%	11.29%
Maturity date	Mar. 22, 2026		Mar. 22, 2026	Mar. 22, 2026	Mar. 22, 2026	Mar. 22, 2026
Principal/Shares	$ 25,404
Investments, amortized cost	25,185
Investments at fair value	$ 25,404
PIK	(6.00%)		(6.00%)	(6.00%)	(6.00%)	(6.00%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:DCBloxIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: DC Blox Inc. Warrants
Investments
Principal/Shares	$ 177
Investments, amortized cost	$ 2
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:DCBloxIncMember
Investment, Type [Extensible Enumeration]	Warrant [Member]		Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Identifier [Axis]: Darcy Partners Equity Interest
Investments
Principal/Shares	$ 359
Investments, amortized cost	359
Investments at fair value	$ 367
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Darcy Partners [Member]
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Darcy Partners First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.75%		7.75%	7.75%	7.75%	7.75%
Interest rate	9.50%		9.50%	9.50%	9.50%	9.50%
Maturity date	Jun. 01, 2028		Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028
Principal/Shares	$ 1,530
Investments, amortized cost	1,515
Investments at fair value	$ 1,515
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Darcy Partners [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Darcy Partners First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Jun. 01, 2028		Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028
Investments at fair value	$ (3)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Darcy Partners [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Datix Bidco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%	4.00%	4.50%	4.50%	4.50%	4.50%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%
Interest rate	4.57%	4.25%	4.57%	4.57%	4.57%	4.57%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%
Maturity date	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025	Apr. 28, 2025
Principal/Shares			$ 42				$ 42
Investments, amortized cost	$ 32						32
Investments at fair value	$ 26						$ 31
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:DatixBidcoLimitedMember	bcsf:DatixBidcoLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember	bcsf:BankBillSwapRateMember
Investment, Identifier [Axis]: Datix Bidco Limited First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		4.50%					4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate		4.96%					4.96%	4.96%	4.96%	4.96%	4.96%	4.96%
Maturity date		Oct. 28, 2024					Oct. 28, 2024	Oct. 28, 2024	Oct. 28, 2024	Oct. 28, 2024	Oct. 28, 2024	Oct. 28, 2024
Principal/Shares | €								€ 10
Investments, amortized cost | €								13
Investments at fair value | €								€ 13
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:DatixBidcoLimitedMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Healthcare And Pharmaceuticals [Member]					Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Datix Bidco Limited Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Interest rate	9.44%	8.21%	9.44%	9.44%	9.44%	9.44%	8.21%	8.21%	8.21%	8.21%	8.21%	8.21%
Maturity date	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026	Apr. 27, 2026
Principal/Shares					£ 121			€ 121
Investments, amortized cost	$ 164							164
Investments at fair value	$ 132							€ 164
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:DatixBidcoLimitedMember	bcsf:DatixBidcoLimitedMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember	London Interbank Offered Rate (LIBOR) [Member]	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc First Lien Senior Secured Loan - Delayed Draw 1
Investments
Spread Above Index (as a percent)	8.50%		8.50%	8.50%	8.50%	8.50%
Interest rate	12.17%		12.17%	12.17%	12.17%	12.17%
Maturity date	Oct. 02, 2023		Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares	$ 3,440
Investments, amortized cost	3,440
Investments at fair value	$ 3,371
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]		Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]		Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc First Lien Senior Secured Loan - Delayed Draw 2
Investments
Spread Above Index (as a percent)	8.50%		8.50%	8.50%	8.50%	8.50%
Interest rate	12.17%		12.17%	12.17%	12.17%	12.17%
Maturity date	Oct. 02, 2023		Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares	$ 1,741
Investments, amortized cost	1,741
Investments at fair value	$ 1,707
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]		Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]		Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc First Lien Senior Secured Loan - Delayed Draw 3
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	8.28%		8.28%	8.28%	8.28%	8.28%
Maturity date	Oct. 02, 2023		Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares	$ 4,125
Investments, amortized cost	4,125
Investments at fair value	$ 4,125
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]		Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]		Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	8.50%	1.00%	8.50%	8.50%	8.50%	8.50%	1.00%	1.00%	1.00%	1.00%	1.00%	1.00%
Interest rate	12.17%	9.50%	12.17%	12.17%	12.17%	12.17%	9.50%	9.50%	9.50%	9.50%	9.50%	9.50%
Maturity date	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares	$ 58,721	$ 57,555
Investments, amortized cost	58,721	57,555
Investments at fair value	$ 57,547	$ 48,347
PIK		(8.28%)					(8.28%)	(8.28%)	(8.28%)	(8.28%)	(8.28%)	(8.28%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	6.50%	6.00%	6.50%	6.50%	6.50%	6.50%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	10.17%	7.00%	10.17%	10.17%	10.17%	10.17%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares	$ 4,841	$ 202
Investments, amortized cost	4,841	202
Investments at fair value	$ 4,841	$ 202
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc First Lien Senior Secured Loan 3
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	Oct. 02, 2023		Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares	$ 202
Investments, amortized cost	202
Investments at fair value	$ 202
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]		Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]		Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc. Equity Interest
Investments
Principal/Shares	$ 68	$ 68
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]	Direct Travel, Inc [Member]	Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Equity Securities [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Identifier [Axis]: Direct Travel, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		1.00%					1.00%	1.00%	1.00%	1.00%	1.00%	1.00%
Interest rate		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date		Oct. 02, 2023					Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares		$ 4,766
Investments, amortized cost		4,766
Investments at fair value		$ 4,766
PIK		(6.30%)					(6.30%)	(6.30%)	(6.30%)	(6.30%)	(6.30%)	(6.30%)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Affiliated Issuer, Noncontrolled [Member]					Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]		Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Consumer Non Controlled Affiliate [Member]					Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)		1.00%					1.00%	1.00%	1.00%	1.00%	1.00%	1.00%
Interest rate		9.50%					9.50%	9.50%	9.50%	9.50%	9.50%	9.50%
Maturity date		Oct. 02, 2023					Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares		$ 3,370
Investments, amortized cost		3,370
Investments at fair value		$ 2,831
PIK		(8.28%)					(8.28%)	(8.28%)	(8.28%)	(8.28%)	(8.28%)	(8.28%)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Affiliated Issuer, Noncontrolled [Member]					Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]		Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Consumer Non Controlled Affiliate [Member]					Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc. First Lien Senior Secured Loan - Delayed Draw 2
Investments
Spread Above Index (as a percent)		1.00%					1.00%	1.00%	1.00%	1.00%	1.00%	1.00%
Interest rate		9.50%					9.50%	9.50%	9.50%	9.50%	9.50%	9.50%
Maturity date		Oct. 02, 2023					Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares		$ 1,710
Investments, amortized cost		1,710
Investments at fair value		$ 1,436
PIK		(8.28%)					(8.28%)	(8.28%)	(8.28%)	(8.28%)	(8.28%)	(8.28%)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Affiliated Issuer, Noncontrolled [Member]					Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]		Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Consumer Non Controlled Affiliate [Member]					Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Direct Travel, Inc. First Lien Senior Secured Loan - Delayed Draw 3
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		7.00%					7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date		Oct. 02, 2023					Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023	Oct. 02, 2023
Principal/Shares		$ 4,125
Investments, amortized cost		4,125
Investments at fair value		$ 4,125
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Affiliated Issuer, Noncontrolled [Member]					Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]	Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Issuer Name [Extensible Enumeration]		Direct Travel, Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Consumer Non Controlled Affiliate [Member]					Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]	Transportation Consumer Non Controlled Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Drilling Info Holdings, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%
Interest rate	7.37%	4.35%	7.37%	7.37%	7.37%	7.37%	4.35%	4.35%	4.35%	4.35%	4.35%	4.35%
Maturity date	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025
Principal/Shares	$ 11,178	$ 22,152
Investments, amortized cost	11,160	22,101
Investments at fair value	$ 10,815	$ 21,930
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:DrillingInfoHoldingsIncMember	bcsf:DrillingInfoHoldingsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Eagle Rock Capital Corporation Preferred Equity
Investments
Principal/Shares	$ 3,345	$ 2,354
Investments, amortized cost	3,345	2,354
Investments at fair value	$ 3,798	$ 2,354
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:EagleRockCapitalCorporationMember	bcsf:EagleRockCapitalCorporationMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: East BCC Coinvest II, LLC Equity Interest
Investments
Principal/Shares	$ 1,419	$ 1,419
Investments, amortized cost	1,419	1,419
Investments at fair value	$ 989	$ 1,065
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:EastBCCCoinvestIILLCMember	bcsf:EastBCCCoinvestIILLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Identifier [Axis]: Efficient Collaborative Retail Marketing Company, LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.25%		5.25%	5.25%	5.25%	5.25%
Interest rate	8.73%		8.73%	8.73%	8.73%	8.73%
Maturity date	Jun. 15, 2024		Jun. 15, 2024	Jun. 15, 2024	Jun. 15, 2024	Jun. 15, 2024
Principal/Shares	$ 1,275
Investments, amortized cost	1,275
Investments at fair value	$ 1,275
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Efficient Collaborative Retail Marketing Company, L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Efficient Collaborative Retail Marketing Company, LLC First Lien Senior Secured Loan - Revolver Libor
Investments
Spread Above Index (as a percent)		5.25%					5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		Jun. 15, 2022					Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022
Principal/Shares		$ 1,275
Investments, amortized cost		1,275
Investments at fair value		$ 1,275
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Efficient Collaborative Retail Marketing Company, L L C [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Media: Diversified & Production					Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Efficient Collaborative Retail Marketing Company, LLC First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	6.75%		6.75%	6.75%	6.75%	6.75%
Interest rate	10.42%		10.42%	10.42%	10.42%	10.42%
Maturity date	Jun. 15, 2024		Jun. 15, 2024	Jun. 15, 2024	Jun. 15, 2024	Jun. 15, 2024
Principal/Shares	$ 15,006
Investments, amortized cost	15,006
Investments at fair value	$ 13,543
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Efficient Collaborative Retail Marketing Company, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Efficient Collaborative Retail Marketing Company, LLC First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	6.75%		6.75%	6.75%	6.75%	6.75%
Interest rate	10.42%		10.42%	10.42%	10.42%	10.42%
Maturity date	Jun. 15, 2024		Jun. 15, 2024	Jun. 15, 2024	Jun. 15, 2024	Jun. 15, 2024
Principal/Shares	$ 9,736
Investments, amortized cost	9,764
Investments at fair value	$ 8,787
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Efficient Collaborative Retail Marketing Company, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Efficient Collaborative Retail Marketing Company, LLC First Lien Senior Secured Loan Libor 1
Investments
Spread Above Index (as a percent)		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Interest rate		7.75%					7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Maturity date		Jun. 15, 2022					Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022
Principal/Shares		$ 15,095
Investments, amortized cost		15,114
Investments at fair value		$ 14,340
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Efficient Collaborative Retail Marketing Company, L L C [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Efficient Collaborative Retail Marketing Company, LLC First Lien Senior Secured Loan Libor 2
Investments
Spread Above Index (as a percent)		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Interest rate		7.75%					7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Maturity date		Jun. 15, 2022					Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022	Jun. 15, 2022
Principal/Shares		$ 9,788
Investments, amortized cost		9,800
Investments at fair value		$ 9,298
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Efficient Collaborative Retail Marketing Company, L L C [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Diversified & Production					Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Electronics For Imaging, Inc. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		9.00%					9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate		9.10%					9.10%	9.10%	9.10%	9.10%	9.10%	9.10%
Maturity date		Jul. 23, 2027					Jul. 23, 2027	Jul. 23, 2027	Jul. 23, 2027	Jul. 23, 2027	Jul. 23, 2027	Jul. 23, 2027
Principal/Shares		$ 12,070
Investments, amortized cost		11,460
Investments at fair value		$ 11,285
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ElectronicsForImagingIncMember
Investment, Type [Extensible Enumeration]		Second Lien Senior Secured Loan [Member]					Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Capital Equipment Sector [Member]					Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Element Buyer, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	8.62%	6.50%	8.62%	8.62%	8.62%	8.62%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025
Principal/Shares	$ 36,721	$ 37,007
Investments, amortized cost	36,878	37,199
Investments at fair value	$ 36,721	$ 37,007
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Element Buyer, Inc [Member]	Element Buyer, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Element Buyer, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	8.62%	6.50%	8.62%	8.62%	8.62%	8.62%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jul. 19, 2025	Jul. 18, 2025	Jul. 19, 2025	Jul. 19, 2025	Jul. 19, 2025	Jul. 19, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025	Jul. 18, 2025
Principal/Shares	$ 10,993	$ 11,078
Investments, amortized cost	11,008	11,097
Investments at fair value	$ 10,993	$ 11,078
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Element Buyer, Inc [Member]	Element Buyer, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Element Buyer, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	8.62%	6.50%	8.62%	8.62%	8.62%	8.62%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024	Jul. 19, 2024
Principal/Shares	$ 850	$ 1,700
Investments, amortized cost	831	1,672
Investments at fair value	$ 850	$ 1,700
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Element Buyer, Inc [Member]	Element Buyer, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Elevator Holdco Inc. Equity Interest
Investments
Principal/Shares	$ 2	$ 2
Investments, amortized cost	2,448	2,448
Investments at fair value	$ 3,083	$ 2,550
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ElevatorHoldcoIncMember	bcsf:ElevatorHoldcoIncMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Eleven Software First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	8.00%		8.00%	8.00%	8.00%	8.00%
Interest rate	11.55%		11.55%	11.55%	11.55%	11.55%
Maturity date	Apr. 25, 2027		Apr. 25, 2027	Apr. 25, 2027	Apr. 25, 2027	Apr. 25, 2027
Principal/Shares	$ 7,439
Investments, amortized cost	7,369
Investments at fair value	$ 7,365
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Eleven Software [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Eleven Software First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Sep. 25, 2026		Sep. 25, 2026	Sep. 25, 2026	Sep. 25, 2026	Sep. 25, 2026
Investments at fair value	$ (15)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Eleven Software [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Eleven Software Preferred Equity
Investments
Principal/Shares	$ 896
Investments, amortized cost	896
Investments at fair value	$ 896
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Eleven Software [Member]
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Elk Parent Holdings, LP Equity Interest
Investments
Principal/Shares	$ 1	$ 1
Investments, amortized cost	12	12
Investments at fair value	$ 487	$ 407
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ElkParentHoldingsLPMember	bcsf:ElkParentHoldingsLPMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Identifier [Axis]: Elk Parent Holdings, LP Preferred Equity
Investments
Principal/Shares	$ 120	$ 120
Investments, amortized cost	1,202	1,202
Investments at fair value	$ 1,514	$ 1,427
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ElkParentHoldingsLPMember	bcsf:ElkParentHoldingsLPMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Identifier [Axis]: Ergotron Acquisition Llc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.89%		8.89%	8.89%	8.89%	8.89%
Maturity date	Jul. 06, 2028		Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028
Principal/Shares	$ 12,250
Investments, amortized cost	12,010
Investments at fair value	$ 12,005
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ErgotronAcquisitionLlcMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Capital Equipment Sector [Member]		Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: FCG Acquisitions, Inc. Preferred Equity
Investments
Principal/Shares	$ 4	$ 4
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:FCGAcquisitionsIncMember	bcsf:FCGAcquisitionsIncMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Identifier [Axis]: FL Hawk Intermediate Holdings, Inc. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate	12.42%	10.00%	12.42%	12.42%	12.42%	12.42%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028
Principal/Shares	$ 15,125	$ 21,125
Investments, amortized cost	14,744	20,543
Investments at fair value	$ 15,125	$ 21,125
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:FLHawkIntermediateHoldingsIncMember	bcsf:FLHawkIntermediateHoldingsIncMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: FNZ UK Finco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	7.76%		7.76%	7.76%	7.76%	7.76%
Maturity date	Sep. 30, 2026		Sep. 30, 2026	Sep. 30, 2026	Sep. 30, 2026	Sep. 30, 2026
Principal/Shares	$ 7,741
Investments, amortized cost	5,276
Investments at fair value	$ 4,830
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:FnzUkFincoLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Fineline Technologies, Inc. Equity Interest
Investments
Principal/Shares	$ 939	$ 939
Investments, amortized cost	939	939
Investments at fair value	$ 1,201	$ 1,241
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:FinelineTechnologiesIncMember	bcsf:FinelineTechnologiesIncMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Identifier [Axis]: Forming Machining Industries Holdings, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%	4.25%
Interest rate	7.37%	4.47%	7.37%	7.37%	7.37%	7.37%	4.47%	4.47%	4.47%	4.47%	4.47%	4.47%
Maturity date	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025	Oct. 09, 2025
Principal/Shares	$ 16,312	$ 16,439
Investments, amortized cost	16,242	16,352
Investments at fair value	$ 14,028	$ 15,288
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:FormingMachiningIndustriesHoldingsLLCMember	bcsf:FormingMachiningIndustriesHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Forming Machining Industries Holdings, LLC Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%
Interest rate	11.37%	8.47%	11.37%	11.37%	11.37%	11.37%	8.47%	8.47%	8.47%	8.47%	8.47%	8.47%
Maturity date	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026	Oct. 09, 2026
Principal/Shares	$ 6,540	$ 6,540
Investments, amortized cost	6,501	6,494
Investments at fair value	$ 5,297	$ 5,821
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:FormingMachiningIndustriesHoldingsLLCMember	bcsf:FormingMachiningIndustriesHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: GSP Holdings LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%	6.75%	9.42%	9.42%	9.42%	9.42%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Nov. 06, 2025	Nov. 06, 2024	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2024	Nov. 06, 2024	Nov. 06, 2024	Nov. 06, 2024	Nov. 06, 2024	Nov. 06, 2024
Principal/Shares	$ 35,548	$ 35,622
Investments, amortized cost	35,523	35,516
Investments at fair value	$ 33,415	$ 32,951
PIK	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GSPHoldingsLLCMember	bcsf:GSPHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: GSP Holdings LLC Senior First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	8.77%	6.75%	8.77%	8.77%	8.77%	8.77%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025	Nov. 06, 2025
Principal/Shares	$ 4,096	$ 1,602
Investments, amortized cost	4,073	1,573
Investments at fair value	$ 3,823	$ 1,261
PIK	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)	(0.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GSPHoldingsLLCMember	bcsf:GSPHoldingsLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Gale Aviation (Offshore) Co Equity Interest
Investments
Principal/Shares	$ 90,450	$ 88,985
Investments, amortized cost	90,450	88,985
Investments at fair value	$ 88,695	$ 72,839
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	Gale Aviation Offshore Co [Member]	Gale Aviation Offshore Co [Member]
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: Gluware First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%		9.00%	9.00%	9.00%	9.00%
Interest rate	12.50%		12.50%	12.50%	12.50%	12.50%
Maturity date	Oct. 15, 2025		Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025
Principal/Shares	$ 19,404
Investments, amortized cost	18,700
Investments at fair value	$ 18,434
PIK	(3.50%)		(3.50%)	(3.50%)	(3.50%)	(3.50%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GluwareMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Gluware T/L First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		12.50%					12.50%	12.50%	12.50%	12.50%	12.50%	12.50%
Interest rate		9.00%					9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Maturity date		Oct. 15, 2025					Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025
Principal/Shares		$ 18,898
Investments, amortized cost		18,534
Investments at fair value		$ 18,520
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:GluwareTLMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Gluware Warrant Warrants
Investments
Principal/Shares		$ 3,328
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:GluwareWarrantMember
Investment, Type [Extensible Enumeration]		Warrant [Member]					Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Gluware Warrants
Investments
Principal/Shares	$ 3,328
Investments, amortized cost	478
Investments at fair value	$ 435
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GluwareMember
Investment, Type [Extensible Enumeration]	Warrant [Member]		Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Goldman Sachs Financial Square Government Fund Institutional Share Class Cash Equivalents
Investments
Interest rate	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%	0.03%
Principal/Shares	$ 31,249	$ 177,554
Investments, amortized cost	31,249	177,554
Investments at fair value	$ 31,249	$ 177,554
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Cash Equivalents [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GoldmanSachsFinancialSquareGovernmentFundInstitutionalShareClassMember	bcsf:GoldmanSachsFinancialSquareGovernmentFundInstitutionalShareClassMember
Investment, Type [Extensible Enumeration]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]
Investment, Industry Sector [Extensible Enumeration]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]	Cash Equivalents [Member]
Investment, Identifier [Axis]: Grammer Investment Holdings LLC Equity Interest
Investments
Principal/Shares	$ 1,011	$ 1,011
Investments, amortized cost	1,011	1,011
Investments at fair value	$ 1,011	$ 1,056
PIK	10.00%		10.00%	10.00%	10.00%	10.00%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GrammerInvestmentHoldingsLLCMember	bcsf:GrammerInvestmentHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: Grammer Investment Holdings LLC Preferred Equity
Investments
Spread Above Index (as a percent)	10.00%		10.00%	10.00%	10.00%	10.00%
Interest rate	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Principal/Shares	$ 9	$ 8
Investments, amortized cost	791	790
Investments at fair value	$ 894	$ 830
PIK		10.00%					10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GrammerInvestmentHoldingsLLCMember	bcsf:GrammerInvestmentHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: Grammer Investment Holdings LLC Warrants
Investments
Principal/Shares	$ 122	$ 122
Investments at fair value	$ 95	$ 126
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:GrammerInvestmentHoldingsLLCMember	bcsf:GrammerInvestmentHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]	Warrant [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: Grammer Purchaser, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%		4.50%	4.50%	4.50%	4.50%
Interest rate	7.57%		7.57%	7.57%	7.57%	7.57%
Maturity date	Sep. 30, 2024		Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024
Principal/Shares	$ 3,843
Investments, amortized cost	3,782
Investments at fair value	$ 3,834
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Grammer Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Grammer Purchaser, Inc First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		4.50%					4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024
Principal/Shares		$ 7,319
Investments, amortized cost		7,202
Investments at fair value	$ (2)	$ 7,319
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Grammer Purchaser, Inc [Member]	Grammer Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Great Expressions Dental Center PC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date		Sep. 28, 2023					Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023
Principal/Shares		$ 7,831
Investments, amortized cost		7,844
Investments at fair value		$ 7,205
PIK		(0.50%)					(0.50%)	(0.50%)	(0.50%)	(0.50%)	(0.50%)	(0.50%)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Great Expressions Dental Center P C [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Healthcare And Pharmaceuticals [Member]					Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Great Expressions Dental Center PC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date		Sep. 28, 2022					Sep. 28, 2022	Sep. 28, 2022	Sep. 28, 2022	Sep. 28, 2022	Sep. 28, 2022	Sep. 28, 2022
Principal/Shares		$ 1,027
Investments, amortized cost		1,025
Investments at fair value		$ 929
PIK		(0.50%)					(0.50%)	(0.50%)	(0.50%)	(0.50%)	(0.50%)	(0.50%)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Great Expressions Dental Center P C [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Healthcare And Pharmaceuticals [Member]					Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Great Expressions Dental Center PC First Lien Senior Secured Loan - Revolver Libor
Investments
Spread Above Index (as a percent)	4.25%		4.25%	4.25%	4.25%	4.25%
Interest rate	7.88%		7.88%	7.88%	7.88%	7.88%
Maturity date	Sep. 28, 2023		Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023
Principal/Shares	$ 986
Investments, amortized cost	983
Investments at fair value	$ 897
PIK	(0.50%)		(0.50%)	(0.50%)	(0.50%)	(0.50%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Great Expressions Dental Center P C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Great Expressions Dental Center PC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	4.25%		4.25%	4.25%	4.25%	4.25%
Interest rate	7.88%		7.88%	7.88%	7.88%	7.88%
Maturity date	Sep. 28, 2023		Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023	Sep. 28, 2023
Principal/Shares	$ 7,868
Investments, amortized cost	7,899
Investments at fair value	$ 7,278
PIK	(0.50%)		(0.50%)	(0.50%)	(0.50%)	(0.50%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Great Expressions Dental Center P C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Green Street Parent, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%	5.75%	5.50%	5.50%	5.50%	5.50%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	8.62%	5.50%	8.62%	8.62%	8.62%	8.62%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026
Principal/Shares	$ 3,411	$ 14,190
Investments, amortized cost	3,369	13,988
Investments at fair value	$ 3,445	$ 14,190
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Green Street Parent, L L C [Member]	Green Street Parent, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Green Street Parent, LLC First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025	Aug. 27, 2025
Investments at fair value	$ 24
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Green Street Parent, L L C [Member]	Green Street Parent, L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]
Investment, Identifier [Axis]: Green Street Parent, LLC First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	5.50%	5.00%	5.50%	5.50%	5.50%	5.50%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate	8.62%	5.50%	8.62%	8.62%	8.62%	8.62%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026
Principal/Shares	$ 4,466	$ 4,500
Investments, amortized cost	4,390	4,411
Investments at fair value	$ 4,511	$ 4,500
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Green Street Parent, L L C [Member]	Green Street Parent, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoan2Member	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member
Investment, Industry Sector [Extensible Enumeration]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Horizon Telcom, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Jun. 15, 2023					Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023
Principal/Shares		$ 13,104
Investments, amortized cost		13,045
Investments at fair value		$ 13,104
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:HorizonTelcomIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Horizon Telcom, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Jun. 15, 2023					Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023
Principal/Shares		$ 890
Investments, amortized cost		888
Investments at fair value		$ 890
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:HorizonTelcomIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Horizon Telcom, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Jun. 15, 2023					Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023	Jun. 15, 2023
Principal/Shares		$ 116
Investments, amortized cost		114
Investments at fair value		$ 116
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:HorizonTelcomIncMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Telecommunications [Member]					Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Insigneo Financial Group LLC Equity Interest
Investments
Investments, amortized cost	$ 2,140
Investments at fair value	$ 2,135
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:InsigneoFinancialGroupLlcMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Identifier [Axis]: Insigneo Financial Group LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.19%		9.19%	9.19%	9.19%	9.19%
Maturity date	Aug. 01, 2028		Aug. 01, 2028	Aug. 01, 2028	Aug. 01, 2028	Aug. 01, 2028
Principal/Shares	$ 3,825
Investments, amortized cost	3,731
Investments at fair value	$ 3,729
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:InsigneoFinancialGroupLlcMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: International Entertainment Investments Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Interest rate	6.47%		6.47%	6.47%	6.47%	6.47%
Maturity date	May 31, 2025		May 31, 2025	May 31, 2025	May 31, 2025	May 31, 2025
Principal/Shares | £					£ 87
Investments, amortized cost	$ 107
Investments at fair value	$ 98
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:InternationalEntertainmentInvestmentsLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: International Entertainment Investments Limited First Lien Senior Secured Loan Gbp libor
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.06%					5.06%	5.06%	5.06%	5.06%	5.06%	5.06%
Maturity date		May 31, 2023					May 31, 2023	May 31, 2023	May 31, 2023	May 31, 2023	May 31, 2023	May 31, 2023
Principal/Shares | £									£ 87
Investments, amortized cost | £									106
Investments at fair value | £									£ 118
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:InternationalEntertainmentInvestmentsLimitedMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Diversified & Production					Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember					bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember
Investment, Identifier [Axis]: International Senior Loan Program, LLC Equity Interest Investment Vehicles
Investments
Principal/Shares	$ 57,774	$ 41,823
Investments, amortized cost	54,892	39,596
Investments at fair value	$ 54,584	$ 44,444
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	International Senior Loan Program L L C [Member]	International Senior Loan Program L L C [Member]
Investment, Type [Extensible Enumeration]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]	Equity Interest Investment Vehicles [Member]
Investment, Industry Sector [Extensible Enumeration]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: International Senior Loan Program, LLC Subordinated Note Investment Vehicles
Investments
Spread Above Index (as a percent)	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%
Interest rate	10.29%	9.00%	10.29%	10.29%	10.29%	10.29%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Maturity date	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028	Feb. 22, 2028
Principal/Shares	$ 173,289	$ 125,437
Investments, amortized cost	173,289	125,437
Investments at fair value	$ 173,289	$ 125,437
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	International Senior Loan Program L L C [Member]	International Senior Loan Program L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember	bcsf:SubordinatedNoteInvestmentVehiclesMember
Investment, Industry Sector [Extensible Enumeration]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]	Investment Vehicles [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Iris Holding, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Interest rate	7.89%		7.89%	7.89%	7.89%	7.89%
Maturity date	Jun. 15, 2028		Jun. 15, 2028	Jun. 15, 2028	Jun. 15, 2028	Jun. 15, 2028
Principal/Shares	$ 13,050
Investments, amortized cost	12,388
Investments at fair value	$ 12,032
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:IrisHoldingInc.Member
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Containers Packaging And Glass [Member]		Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Island Medical Management Holdings, LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date		Sep. 01, 2023					Sep. 01, 2023	Sep. 01, 2023	Sep. 01, 2023	Sep. 01, 2023	Sep. 01, 2023	Sep. 01, 2023
Principal/Shares		$ 8,520
Investments, amortized cost		8,496
Investments at fair value		$ 8,371
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:IslandMedicalManagementHoldingsLLCMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Healthcare And Pharmaceuticals [Member]					Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: JHCC Holdings, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%	6.75%	9.42%	9.42%	9.42%	9.42%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025
Principal/Shares	$ 21,318	$ 29,081
Investments, amortized cost	21,148	28,799
Investments at fair value	$ 20,679	$ 29,081
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:JHCCHoldingsLLCMember	bcsf:JHCCHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: JHCC Holdings, LLC First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.75%	4.50%	5.75%	5.75%	5.75%	5.75%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate	9.42%	7.75%	9.42%	9.42%	9.42%	9.42%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Maturity date		Sep. 09, 2025					Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025
Principal/Shares	$ 8,353	$ 2,635
Investments, amortized cost	8,328	2,618
Investments at fair value	$ 8,103	$ 2,635
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:JHCCHoldingsLLCMember	bcsf:JHCCHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	us-gaap:PrimeRateMember	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: JHCC Holdings, LLC First Lien Senior Secured Loan - Delayed Draw 2
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Sep. 09, 2025					Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025
Principal/Shares		$ 5,782
Investments, amortized cost		5,776
Investments at fair value		$ 5,782
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:JHCCHoldingsLLCMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Automotive Sector [Member]					Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: JHCC Holdings, LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%	6.75%	9.42%	9.42%	9.42%	9.42%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025
Principal/Shares	$ 1,620	$ 894
Investments, amortized cost	1,592	863
Investments at fair value	$ 1,535	$ 894
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:JHCCHoldingsLLCMember	bcsf:JHCCHoldingsLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	us-gaap:PrimeRateMember	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: Jonathan Acquisition Company Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate	12.60%	10.00%	12.60%	12.60%	12.60%	12.60%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027
Principal/Shares	$ 8,000	$ 8,000
Investments, amortized cost	7,836	7,821
Investments at fair value	$ 8,000	$ 8,000
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:JonathanAcquisitionCompanyMember	bcsf:JonathanAcquisitionCompanyMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Kellstrom Aerospace Group, Inc Equity Interest
Investments
Principal/Shares	$ 1	$ 1
Investments, amortized cost	1,963	1,963
Investments at fair value	$ 792	$ 913
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:KellstromAerospaceGroupIncMember	bcsf:KellstromAerospaceGroupIncMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: Kellstrom Commercial Aerospace, Inc First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.25%	5.50%	6.25%	6.25%	6.25%	6.25%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	11.25%	6.50%	11.25%	11.25%	11.25%	11.25%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025
Principal/Shares	$ 2,666	$ 2,239
Investments, amortized cost	2,626	2,176
Investments at fair value	$ 2,410	$ 1,919
PIK	(0.50%)		(0.50%)	(0.50%)	(0.50%)	(0.50%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Kellstrom Commercial Aerospace, Inc [Member]	Kellstrom Commercial Aerospace, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Kellstrom Commercial Aerospace, Inc First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	6.00%	5.50%	6.00%	6.00%	6.00%	6.00%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	8.37%	6.50%	8.37%	8.37%	8.37%	8.37%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025	Jul. 01, 2025
Principal/Shares	$ 30,082	$ 32,855
Investments, amortized cost	29,772	32,430
Investments at fair value	$ 28,277	$ 30,884
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Kellstrom Commercial Aerospace, Inc [Member]	Kellstrom Commercial Aerospace, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Learning Pool First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	3.00%		3.00%	3.00%	3.00%	3.00%
Interest rate	9.18%		9.18%	9.18%	9.18%	9.18%
Maturity date	Jul. 07, 2028		Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028
Principal/Shares | €				€ 279
Investments, amortized cost	$ 360
Investments at fair value	$ 312
PIK	(4.25%)		(4.25%)	(4.25%)	(4.25%)	(4.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:LearningPoolMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Learning Pool First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	3.00%		3.00%	3.00%	3.00%	3.00%
Interest rate	9.18%		9.18%	9.18%	9.18%	9.18%
Maturity date	Jul. 07, 2028		Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028	Jul. 07, 2028
Principal/Shares | £					£ 100
Investments, amortized cost	$ 129
Investments at fair value	$ 111
PIK	(4.25%)		(4.25%)	(4.25%)	(4.25%)	(4.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:LearningPoolMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Lightning Finco Limited First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	6.25%		6.25%	6.25%	6.25%	6.25%
Maturity date	Sep. 01, 2028		Sep. 01, 2028	Sep. 01, 2028	Sep. 01, 2028	Sep. 01, 2028
Principal/Shares	$ 1,300
Investments, amortized cost	1,417
Investments at fair value	$ 1,274
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:LightningFincoLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Broadcasting & Subscription		Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Lightning Finco Limited First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	5.50%	5.75%	5.50%	5.50%	5.50%	5.50%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	8.57%	6.50%	8.57%	8.57%	8.57%	8.57%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Sep. 01, 2028	Jul. 14, 2028	Sep. 01, 2028	Sep. 01, 2028	Sep. 01, 2028	Sep. 01, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028
Principal/Shares	$ 1,443	$ 4,350
Investments, amortized cost	1,408	4,234
Investments at fair value	$ 1,443	$ 4,350
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:LightningFincoLimitedMember	bcsf:LightningFincoLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Lightning Finco Limited First Lien Senior Secured Loan Libor 1
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date		Jul. 14, 2028					Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028	Jul. 14, 2028
Principal/Shares		$ 4,629
Investments, amortized cost		4,506
Investments at fair value		$ 4,629
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:LightningFincoLimitedMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Broadcasting & Subscription					Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription	Media: Broadcasting & Subscription
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Lightning Holdings B, LLC Equity Interest
Investments
Principal/Shares	$ 23,355	$ 13,843
Investments, amortized cost	23,665	14,152
Investments at fair value	$ 25,101	$ 14,851
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]	Investment, Affiliated Issuer, Controlled [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:LightningHoldingsBLLCMember	bcsf:LightningHoldingsBLLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]	Transportation Cargo Controlled Affiliate [Member]
Investment, Identifier [Axis]: MRH Trowe Beteiligungsgesellschaft MBH First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Interest rate	6.50%		6.50%	6.50%	6.50%	6.50%
Maturity date	Jul. 26, 2028		Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028
Principal/Shares | £					£ 1,865
Investments, amortized cost	$ 1,858
Investments at fair value	$ 1,828
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Margaux U K Finance Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: MRHT Facility A First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date		Jul. 26, 2028					Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028
Principal/Shares | €								€ 216
Investments, amortized cost | €								248
Investments at fair value | €								€ 245
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:MRHTFacilityAMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:EuroInterbankOfferRateMember					bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: MRHT First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	5.50%		5.50%	5.50%	5.50%	5.50%
Maturity date	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028
Principal/Shares | €				€ 500
Investments, amortized cost	$ 535
Investments at fair value	$ 485
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MRHTMember	bcsf:MRHTAcquisitionFacilityMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: MRHT First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	5.70%		5.70%	5.70%	5.70%	5.70%
Maturity date	Jul. 26, 2028		Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028
Principal/Shares | €				€ 216
Investments, amortized cost	$ 249
Investments at fair value	$ 209
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MRHTMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: MRHT First Lien Senior Secured Loan 3
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	5.50%		5.50%	5.50%	5.50%	5.50%
Maturity date	Jul. 26, 2028		Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028	Jul. 26, 2028
Principal/Shares | €				€ 10,000
Investments, amortized cost	$ 10,125
Investments at fair value	$ 9,704
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MRHTMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: MRI Software LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%	6.50%	9.17%	9.17%	9.17%	9.17%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026
Principal/Shares	$ 25,728	$ 25,926
Investments, amortized cost	25,667	25,850
Investments at fair value	$ 25,004	$ 25,926
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MRISoftwareLLCMember	bcsf:MRISoftwareLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: MRI Software LLC First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026	Feb. 10, 2026
Investments, amortized cost	$ 52	$ 48
Investments at fair value	$ (50)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MRISoftwareLLCMember	bcsf:MRISoftwareLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: MZR Aggregator Equity Interest
Investments
Principal/Shares	$ 1	$ 1
Investments, amortized cost	798	798
Investments at fair value	$ 791	$ 798
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MZRAggregatorMember	bcsf:MZRAggregatorMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Identifier [Axis]: MZR Buyer, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Interest rate	10.42%	7.75%	10.42%	10.42%	10.42%	10.42%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Maturity date	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026
Principal/Shares	$ 16,849	$ 40,228
Investments, amortized cost	16,651	39,551
Investments at fair value	$ 16,849	$ 40,228
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MZRBuyerLLCMember	bcsf:MZRBuyerLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: MZR Buyer, LLC First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MZRBuyerLLCMember	bcsf:MZRBuyerLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Mach Acquisition R/C Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	7.50%		7.50%	7.50%	7.50%	7.50%
Interest rate	10.11%		10.11%	10.11%	10.11%	10.11%
Maturity date	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026
Principal/Shares	$ 3,013
Investments, amortized cost	2,850
Investments at fair value	$ 2,410	$ (201)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Mach Acquisition R C [Member]	Mach Acquisition R C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Mach Acquisition T/L First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Interest rate	10.24%	8.50%	10.24%	10.24%	10.24%	10.24%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Maturity date	Oct. 18, 2026		Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026	Oct. 18, 2026
Principal/Shares	$ 33,143	$ 32,640
Investments, amortized cost	32,602	32,006
Investments at fair value	$ 31,154	$ 31,987
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MachAcquisitionTLMember	bcsf:MachAcquisitionTLMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Margaux Acquisition Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date		Dec. 19, 2024					Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares		$ 28,334
Investments, amortized cost		28,000
Investments at fair value		$ 28,334
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Margaux Acquisition Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Margaux Acquisition Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date		Dec. 19, 2024					Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares		$ 9,198
Investments, amortized cost		9,173
Investments at fair value		$ 9,198
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Margaux Acquisition Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Margaux Acquisition Inc. First Lien Senior Secured Loan - Delayed Draw Libor
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.03%		8.03%	8.03%	8.03%	8.03%
Maturity date	Dec. 19, 2024		Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares	$ 9,128
Investments, amortized cost	9,109
Investments at fair value	$ 9,083
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Margaux Acquisition Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Margaux Acquisition Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.03%		8.03%	8.03%	8.03%	8.03%
Maturity date	Dec. 19, 2024		Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares	$ 17,637
Investments, amortized cost	17,472
Investments at fair value	$ 17,548
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Margaux Acquisition Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Margaux Acquisition, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Investments at fair value	$ (14)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Margaux Acquisition Inc [Member]	Margaux Acquisition Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Identifier [Axis]: Margaux UK Finance Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.50%	5.75%	5.75%	5.75%	5.75%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	7.06%	6.50%	7.06%	7.06%	7.06%	7.06%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares	$ 7,512								£ 7,551
Investments, amortized cost	9,697								9,740
Investments at fair value	$ 8,307								£ 10,218
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Margaux U K Finance Limited [Member]	Margaux U K Finance Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember
Investment, Identifier [Axis]: Margaux UK Finance Limited First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares | £									£ 89
Investments, amortized cost | £									112
Investments at fair value	$ (6)								£ 120
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Margaux U K Finance Limited [Member]	Margaux U K Finance Limited [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		us-gaap:LondonInterbankOfferedRateLiborSwapRateMember					us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember	us-gaap:LondonInterbankOfferedRateLiborSwapRateMember
Investment, Identifier [Axis]: Meriplex Communications, Ltd. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	7.95%		7.95%	7.95%	7.95%	7.95%
Maturity date	Jul. 17, 2028		Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028
Principal/Shares	$ 15,294
Investments, amortized cost	15,009
Investments at fair value	$ 14,988
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Meriplex Communications Ltd. [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Meriplex Communications, Ltd. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	7.95%		7.95%	7.95%	7.95%	7.95%
Maturity date	Jul. 17, 2028		Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028
Principal/Shares	$ 2,353
Investments, amortized cost	2,234
Investments at fair value	$ 2,231
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Meriplex Communications Ltd. [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Meriplex Communications, Ltd. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	8.18%		8.18%	8.18%	8.18%	8.18%
Maturity date	Jul. 17, 2028		Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028
Principal/Shares	$ 188
Investments, amortized cost	134
Investments at fair value	$ 132
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Meriplex Communications Ltd. [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Mertus 522. GmbH First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Interest rate	8.11%	6.25%	8.11%	8.11%	8.11%	8.11%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026
Principal/Shares | €				€ 131				€ 225
Investments, amortized cost	$ 142							247
Investments at fair value	$ 126							€ 255
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Mertus522GmbHMember	bcsf:Mertus522GmbHMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Mertus 522. GmbH First Lien Senior Secured Loan - Delayed Draw Euibor
Investments
Spread Above Index (as a percent)		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		May 28, 2026					May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026
Principal/Shares | €								€ 131
Investments, amortized cost | €								142
Investments at fair value | €								€ 149
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Mertus522GmbHMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Healthcare And Pharmaceuticals [Member]					Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:EuroInterbankOfferRateMember					bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Mertus 522. GmbH First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	6.25%		6.25%	6.25%	6.25%	6.25%
Maturity date	May 28, 2026		May 28, 2026	May 28, 2026	May 28, 2026	May 28, 2026
Principal/Shares | €				€ 225
Investments, amortized cost	$ 247
Investments at fair value	$ 216
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Mertus522GmbHMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Morrow Sodali First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Apr. 25, 2028		Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028
Investments at fair value	$ (40)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Morrow Sodali [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Banking Finance Insurance And Real Estate Sector [Member]		Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]
Investment, Identifier [Axis]: Morrow Sodali First Lien Senior Secured Loan - Delayed Draw 2
Investments
Maturity date	Apr. 25, 2028		Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028
Investments at fair value	$ (34)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Morrow Sodali [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Banking Finance Insurance And Real Estate Sector [Member]		Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]
Investment, Identifier [Axis]: Morrow Sodali First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	8.65%		8.65%	8.65%	8.65%	8.65%
Maturity date	Apr. 25, 2028		Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028
Principal/Shares	$ 266
Investments, amortized cost	236
Investments at fair value	$ 234
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Morrow Sodali [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Banking Finance Insurance And Real Estate Sector [Member]		Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Music Creation Group Bidco GmbH First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.39%		9.39%	9.39%	9.39%	9.39%
Maturity date	Aug. 03, 2027		Aug. 03, 2027	Aug. 03, 2027	Aug. 03, 2027	Aug. 03, 2027
Principal/Shares	$ 4,065
Investments, amortized cost	3,974
Investments at fair value	$ 4,014
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:MusicCreationGroupBidcoGmbHMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Diversified & Production		Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production	Media: Diversified & Production
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: NPC International, Inc. Equity Interest
Investments
Principal/Shares	$ 428	$ 564
Investments, amortized cost	639	843
Investments at fair value	$ 121	$ 228
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:NPCInternationalIncMember	bcsf:NPCInternationalIncMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]	Beverage Foodand Tobacco Sector [Member]
Investment, Identifier [Axis]: New Era Cap Co., Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date		Sep. 10, 2023					Sep. 10, 2023	Sep. 10, 2023	Sep. 10, 2023	Sep. 10, 2023	Sep. 10, 2023	Sep. 10, 2023
Principal/Shares		$ 9,970
Investments, amortized cost		9,970
Investments at fair value		$ 9,970
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:NewEraCapCoIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Consumer Goods Non Durable Sector [Member]					Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: New Look (Delaware) Corporation First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%		9.17%	9.17%	9.17%	9.17%
Maturity date	May 26, 2028		May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028
Principal/Shares	$ 9,677
Investments, amortized cost	9,590
Investments at fair value	$ 9,580
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	New Look (Delaware) Corporation [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: New Look (Delaware) Corporation First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	May 26, 2028		May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028
Principal/Shares	$ 386
Investments, amortized cost	376
Investments at fair value	$ 363
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	New Look (Delaware) Corporation [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: New Look Vision Group First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.67%	6.25%	9.67%	9.67%	9.67%	9.67%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028
Principal/Shares						$ 81				$ 322
Investments, amortized cost	$ 64									310
Investments at fair value	$ 58									$ 322
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	New Look Vision Group [Member]	New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: New Look Vision Group First Lien Senior Secured Loan - Delayed Draw Cdor
Investments
Spread Above Index (as a percent)		5.25%					5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		May 26, 2028					May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028
Principal/Shares										$ 2,380
Investments, amortized cost										1,868
Investments at fair value										$ 1,883
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:CanadianDollarOfferedRateMember					bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: New Look Vision Group First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	May 26, 2026		May 26, 2026	May 26, 2026	May 26, 2026	May 26, 2026
Principal/Shares						$ 1,419
Investments, amortized cost	$ 1,055
Investments at fair value	$ 1,009
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:CanadianDollarOfferedRateMember		bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: New Look Vision Group First Lien Senior Secured Loan - Revolver Cdor
Investments
Spread Above Index (as a percent)		5.25%					5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		May 26, 2026					May 26, 2026	May 26, 2026	May 26, 2026	May 26, 2026	May 26, 2026	May 26, 2026
Principal/Shares										$ 313
Investments, amortized cost										228
Investments at fair value										$ 248
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:CanadianDollarOfferedRateMember					bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: New Look Vision Group First Lien Senior Secured Loan Cdor
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		May 26, 2028					May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028	May 26, 2028
Principal/Shares										$ 9,750
Investments, amortized cost										9,653
Investments at fair value										$ 9,750
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:CanadianDollarOfferedRateMember					bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: New Milani Group LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%	6.50%	6.00%	6.00%	6.00%	6.00%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate	9.67%	7.50%	9.67%	9.67%	9.67%	9.67%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date		Jun. 06, 2024					Jun. 06, 2024	Jun. 06, 2024	Jun. 06, 2024	Jun. 06, 2024	Jun. 06, 2024	Jun. 06, 2024
Principal/Shares	$ 21,531	$ 16,752
Investments, amortized cost	21,039	16,678
Investments at fair value	$ 21,100	$ 16,250
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:NewMilaniGroupLLCMember	bcsf:NewMilaniGroupLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: OGH Bidco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	8.53%		8.53%	8.53%	8.53%	8.53%
Maturity date	Jun. 29, 2029		Jun. 29, 2029	Jun. 29, 2029	Jun. 29, 2029	Jun. 29, 2029
Principal/Shares | £					£ 13,299
Investments, amortized cost	$ 15,685
Investments at fair value	$ 14,706
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	OGH Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media Publishing [Member]		Media Publishing [Member]	Media Publishing [Member]	Media Publishing [Member]	Media Publishing [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: OGH Bidco Limited First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Jun. 29, 2029		Jun. 29, 2029	Jun. 29, 2029	Jun. 29, 2029	Jun. 29, 2029
Investments at fair value	$ (69)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	OGH Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Media Publishing [Member]		Media Publishing [Member]	Media Publishing [Member]	Media Publishing [Member]	Media Publishing [Member]
Investment, Identifier [Axis]: OGH Bidco Limited First Lien Senior Secured Loan - Delayed Draw SONIA
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	7.44%		7.44%	7.44%	7.44%	7.44%
Maturity date	Jun. 29, 2029		Jun. 29, 2029	Jun. 29, 2029	Jun. 29, 2029	Jun. 29, 2029
Principal/Shares | £					£ 5,172
Investments, amortized cost	$ 5,893
Investments at fair value	$ 5,719
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	OGH Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Media Publishing [Member]		Media Publishing [Member]	Media Publishing [Member]	Media Publishing [Member]	Media Publishing [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Omni Intermediate DD T/L First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Nov. 23, 2026					Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026
Principal/Shares		$ 776
Investments, amortized cost		769
Investments at fair value		$ 768
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:OmniIntermediateDDTL1Member
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Cargo [Member]					Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Omni Intermediate DD T/L First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Nov. 23, 2026					Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026
Principal/Shares		$ 46
Investments, amortized cost		37
Investments at fair value		$ 37
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:OmniIntermediateDDTL2Member
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Cargo [Member]					Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Omni Intermediate First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	8.69%		8.69%	8.69%	8.69%	8.69%
Maturity date	Nov. 23, 2026		Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026
Principal/Shares	$ 814
Investments, amortized cost	815
Investments at fair value	$ 807
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:OmniIntermediateMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Omni Intermediate First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	6.00%		6.00%	6.00%	6.00%	6.00%
Maturity date	Nov. 23, 2026		Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026
Principal/Shares	$ 366
Investments, amortized cost	359
Investments at fair value	$ 366
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:OmniIntermediateMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Omni Intermediate First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Nov. 30, 2026		Nov. 30, 2026	Nov. 30, 2026	Nov. 30, 2026	Nov. 30, 2026
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:OmniIntermediateMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: Omni Intermediate Holdings Closing Date Term Loan First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Nov. 23, 2026					Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026
Principal/Shares		$ 7,306
Investments, amortized cost		7,233
Investments at fair value		$ 7,233
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:OmniIntermediateHoldingsClosingDateTermLoanMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Transportation Cargo [Member]					Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Omni Intermediate R/C First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Nov. 23, 2025					Nov. 23, 2025	Nov. 23, 2025	Nov. 23, 2025	Nov. 23, 2025	Nov. 23, 2025	Nov. 23, 2025
Principal/Shares		$ 183
Investments, amortized cost		183
Investments at fair value		$ 176
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Omni Intermediate R C [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Transportation Cargo [Member]					Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Omni Logistics, LLC Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate	12.69%	10.00%	12.69%	12.69%	12.69%	12.69%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027
Principal/Shares	$ 8,770	$ 13,770
Investments, amortized cost	8,668	13,527
Investments at fair value	$ 8,770	$ 13,770
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:OmniLogisticsLLCMember	bcsf:OmniLogisticsLLCMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Opus 2 First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date		May 05, 2028					May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Opus2Member
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Opus 2 First Lien Senior Secured Loan Sonia
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		5.55%					5.55%	5.55%	5.55%	5.55%	5.55%	5.55%
Maturity date		May 05, 2028					May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028
Principal/Shares | £									£ 123
Investments, amortized cost | £									167
Investments at fair value | £									£ 166
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Opus2Member
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:SterlingOvernightInterbankAverageRateMember					bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Opus2 Equity Interest
Investments
Principal/Shares	$ 2,272	$ 1,460
Investments, amortized cost	2,900	1,769
Investments at fair value	$ 2,880	$ 2,373
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Opus2Member	bcsf:Opus2Member
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Opus2 First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.28%		5.28%	5.28%	5.28%	5.28%
Interest rate	5.97%		5.97%	5.97%	5.97%	5.97%
Maturity date	May 05, 2028		May 05, 2028	May 05, 2028	May 05, 2028	May 05, 2028
Principal/Shares	$ 123
Investments, amortized cost	167
Investments at fair value	$ 137
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Opus2Member
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: PPX Class A Units Preferred Equity
Investments
Principal/Shares		$ 33
Investments at fair value		$ 163
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:PPXClassAUnitsMember
Investment, Type [Extensible Enumeration]		Preferred Stock [Member]					Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Hospitality Holdings [Member]					Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]
Investment, Identifier [Axis]: PPX Class B Units Preferred Equity
Investments
Principal/Shares		$ 33
Investments, amortized cost		5,000
Investments at fair value		$ 5,279
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:PPXClassBUnitsMember
Investment, Type [Extensible Enumeration]		Preferred Stock [Member]					Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Hospitality Holdings [Member]					Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]
Investment, Identifier [Axis]: PPX Preferred Equity 1
Investments
Principal/Shares	$ 33
Investments at fair value	$ 163
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:PPXMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Hospitality Holdings [Member]		Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]
Investment, Identifier [Axis]: PPX Preferred Equity 2
Investments
Principal/Shares	$ 33
Investments, amortized cost	5,000
Investments at fair value	$ 5,678
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:PPXMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Hospitality Holdings [Member]		Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]	Hospitality Holdings [Member]
Investment, Identifier [Axis]: Paisley Bidco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	6.93%		6.93%	6.93%	6.93%	6.93%
Maturity date	Nov. 26, 2028		Nov. 26, 2028	Nov. 26, 2028	Nov. 26, 2028	Nov. 26, 2028
Principal/Shares | €				€ 3,676
Investments, amortized cost	$ 4,336
Investments at fair value	$ 4,106
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Paisley Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Paisley Bidco Limited First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date		Nov. 24, 2028					Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028
Investments at fair value | €								€ (86)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Paisley Bidco Limited [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Identifier [Axis]: Paisley Bidco Limited First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	6.19%		6.19%	6.19%	6.19%	6.19%
Maturity date	Nov. 26, 2028		Nov. 26, 2028	Nov. 26, 2028	Nov. 26, 2028	Nov. 26, 2028
Principal/Shares | £					£ 32
Investments, amortized cost	$ 36
Investments at fair value	$ 31
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Paisley Bidco Limited [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Paisley Bidco Limited First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date		Nov. 24, 2028					Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028	Nov. 24, 2028
Principal/Shares | £									£ 3,210
Investments, amortized cost | £									3,583
Investments at fair value | £									£ 3,614
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Paisley Bidco Limited [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:EuroInterbankOfferRateMember					bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Parcel 2 Go Acquisition Facility First Lien Senior Secured Loan Sonia
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		5.92%					5.92%	5.92%	5.92%	5.92%	5.92%	5.92%
Maturity date		Jul. 15, 2028					Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028
Principal/Shares | £									£ 3,863
Investments, amortized cost | £									4,982
Investments at fair value | £									£ 5,183
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Parcel2 Go Acquisition Facility [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:SterlingOvernightInterbankAverageRateMember					bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Parcel 2 Go Facility B First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		5.80%					5.80%	5.80%	5.80%	5.80%	5.80%	5.80%
Maturity date		Jul. 15, 2028					Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028
Principal/Shares | £									£ 125
Investments, amortized cost | £									169
Investments at fair value | £									£ 169
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Parcel2GoFacilityBMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:SterlingOvernightInterbankAverageRateMember					bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Parcel 2 Go Shares Equity Interest
Investments
Principal/Shares		$ 2,881
Investments, amortized cost		3,983
Investments at fair value		$ 3,899
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:Parcel2GoSharesMember
Investment, Type [Extensible Enumeration]		Common Stock [Member]					Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Parcel2Go Equity Interest
Investments
Principal/Shares | €				€ 3,605
Investments, amortized cost	$ 4,237
Investments at fair value	$ 3,462
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Parcel2GoMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Parcel2Go First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	7.44%		7.44%	7.44%	7.44%	7.44%
Maturity date	Jul. 15, 2028		Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028
Principal/Shares	$ 39
Investments, amortized cost	50
Investments at fair value	$ 43
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Parcel2GoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Parcel2Go First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	7.94%		7.94%	7.94%	7.94%	7.94%
Maturity date	Jul. 15, 2028		Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028	Jul. 15, 2028
Principal/Shares | £					£ 125
Investments, amortized cost	$ 169
Investments at fair value	$ 140
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:Parcel2GoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Parmenion First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	6.69%		6.69%	6.69%	6.69%	6.69%
Maturity date	May 11, 2029		May 11, 2029	May 11, 2029	May 11, 2029	May 11, 2029
Principal/Shares | £					£ 328
Investments, amortized cost	$ 408
Investments at fair value	$ 366
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ParmenionMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: PetroChoice Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Aug. 19, 2022					Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022
Principal/Shares		$ 9,740
Investments, amortized cost		9,721
Investments at fair value		$ 9,327
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:PetroChoiceHoldingsIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Wholesale					Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: PetroChoice Holdings, Inc. First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)		5.00%					5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Maturity date		Aug. 19, 2022					Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022	Aug. 19, 2022
Principal/Shares		$ 6,445
Investments, amortized cost		6,412
Investments at fair value		$ 6,171
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:PetroChoiceHoldingsIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Wholesale					Wholesale	Wholesale	Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Precision Ultimate Holdings, LLC Equity Interest
Investments
Principal/Shares	$ 1,417	$ 1,417
Investments, amortized cost	1,417	1,417
Investments at fair value	$ 1,401	$ 1,204
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:PrecisionUltimateHoldingsLLCMember	bcsf:PrecisionUltimateHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: Premier Imaging, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.87%		8.87%	8.87%	8.87%	8.87%
Maturity date	Jan. 02, 2025		Jan. 02, 2025	Jan. 02, 2025	Jan. 02, 2025	Jan. 02, 2025
Principal/Shares	$ 7,159
Investments, amortized cost	7,074
Investments at fair value	$ 7,087
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Premier Imaging, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Premier Imaging, LLC First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.87%		8.87%	8.87%	8.87%	8.87%
Maturity date	Jan. 02, 2025		Jan. 02, 2025	Jan. 02, 2025	Jan. 02, 2025	Jan. 02, 2025
Principal/Shares	$ 1,941
Investments, amortized cost	1,863
Investments at fair value	$ 1,873
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Premier Imaging, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Quidditch Acquisition, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.00%		7.00%	7.00%	7.00%	7.00%
Interest rate	9.52%		9.52%	9.52%	9.52%	9.52%
Maturity date	Mar. 21, 2025		Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025
Principal/Shares	$ 9,104
Investments, amortized cost	9,154
Investments at fair value	$ 9,058
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:QuidditchAcquisitionIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Quidditch Acquisition, Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		7.00%					7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Interest rate		8.00%					8.00%	8.00%	8.00%	8.00%	8.00%	8.00%
Maturity date		Mar. 21, 2025					Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025
Principal/Shares		$ 18,636
Investments, amortized cost		18,626
Investments at fair value		$ 18,392
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:QuidditchAcquisitionIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Hotel, Gaming & Leisure					Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: REP Coinvest III- A Omni, LP Equity Interest
Investments
Principal/Shares	$ 1,377	$ 1,377
Investments, amortized cost	1,377	1,377
Investments at fair value	$ 3,568	$ 2,616
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:REPCoinvestIII-AOmniLPMember	bcsf:REPCoinvestIII-AOmniLPMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Equity Securities [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Identifier [Axis]: Reconomy First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	8.44%		8.44%	8.44%	8.44%	8.44%
Maturity date	Jun. 24, 2029		Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029
Principal/Shares | £					£ 6,118
Investments, amortized cost	$ 7,431
Investments at fair value	$ 6,834
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Reconomy [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Reconomy First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	7.19%		7.19%	7.19%	7.19%	7.19%
Maturity date	Jun. 24, 2029		Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029
Principal/Shares	$ 2,467
Investments, amortized cost	2,578
Investments at fair value	$ 2,418
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Reconomy [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Reconomy First Lien Senior Secured Loan 3
Investments
Maturity date	Jun. 24, 2029		Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Reconomy [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Identifier [Axis]: Reconomy First Lien Senior Secured Loan 4
Investments
Maturity date	Jun. 24, 2029		Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029	Jun. 24, 2029
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Reconomy [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Identifier [Axis]: Refine Intermediate, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate	8.17%	5.50%	8.17%	8.17%	8.17%	8.17%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027
Principal/Shares		$ 21,894			£ 1,094
Investments, amortized cost	$ 1,154	21,467
Investments at fair value	$ 1,094	$ 21,894
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Refine Intermediate, Inc [Member]	Refine Intermediate, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember	London Interbank Offered Rate (LIBOR) [Member]	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Refine Intermediate, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026	Sep. 03, 2026
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Refine Intermediate, Inc [Member]	Refine Intermediate, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember		bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember
Investment, Identifier [Axis]: Regan Development Holdings Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.00%	6.50%	7.00%	7.00%	7.00%	7.00%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Apr. 18, 2023	Apr. 18, 2022	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022
Principal/Shares		$ 2,087		€ 2,087
Investments, amortized cost	$ 2,274	2,274
Investments at fair value	$ 1,979	$ 2,326
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ReganDevelopmentHoldingsLimitedMember	bcsf:ReganDevelopmentHoldingsLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Regan Development Holdings Limited First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	7.00%	6.50%	7.00%	7.00%	7.00%	7.00%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Apr. 18, 2023	Apr. 18, 2022	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022
Principal/Shares		$ 677		€ 677
Investments, amortized cost	$ 768	768
Investments at fair value	$ 642	$ 754
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ReganDevelopmentHoldingsLimitedMember	bcsf:ReganDevelopmentHoldingsLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoan2Member	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Regan Development Holdings Limited First Lien Senior Secured Loan 3
Investments
Spread Above Index (as a percent)	7.00%	6.50%	7.00%	7.00%	7.00%	7.00%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Interest rate	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Apr. 18, 2023	Apr. 18, 2022	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2023	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022	Apr. 18, 2022
Principal/Shares		$ 6,335		€ 6,335
Investments, amortized cost	$ 6,868	6,895
Investments at fair value	$ 5,977	$ 7,041
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ReganDevelopmentHoldingsLimitedMember	bcsf:ReganDevelopmentHoldingsLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Revalize, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%		9.42%	9.42%	9.42%	9.42%
Maturity date	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027
Principal/Shares	$ 5,371
Investments, amortized cost	5,325
Investments at fair value	$ 5,331	$ (134)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Revalize, Inc [Member]	Revalize, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Revalize, Inc. First Lien Senior Secured Loan - Delayed Draw 2
Investments
Maturity date	Apr. 15, 2027		Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027
Investments at fair value	$ (98)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Revalize, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Revalize, Inc. First Lien Senior Secured Loan - Delayed Draw Libor
Investments
Spread Above Index (as a percent)		5.25%					5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date		Apr. 15, 2027					Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027
Principal/Shares		$ 5,130
Investments, amortized cost		5,079
Investments at fair value		$ 5,079
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		Revalize, Inc [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Revalize, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%		9.42%	9.42%	9.42%	9.42%
Maturity date	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027	Apr. 15, 2027
Principal/Shares	$ 1,340
Investments, amortized cost	1,329
Investments at fair value	$ 1,330	$ (13)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Revalize, Inc [Member]	Revalize, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: RoC Opco LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	8.50%		8.50%	8.50%	8.50%	8.50%
Interest rate	11.49%		11.49%	11.49%	11.49%	11.49%
Maturity date	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025
Principal/Shares	$ 7,510
Investments, amortized cost	7,423
Investments at fair value	$ 7,485
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:RoCOpcoLLCMember	bcsf:RoCOpcoLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: RoC Opco LLCFirst Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Interest rate	12.17%	9.50%	12.17%	12.17%	12.17%	12.17%	9.50%	9.50%	9.50%	9.50%	9.50%	9.50%
Maturity date	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025
Principal/Shares	$ 15,080	$ 40,079
Investments, amortized cost	14,907	39,486
Investments at fair value	$ 15,042	$ 40,079
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:RoCOpcoLLCMember	bcsf:RoCOpcoLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Robinson Helicopter Equity Interest
Investments
Principal/Shares	$ 1,592
Investments, amortized cost	1,592
Investments at fair value	$ 1,592
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:RobinsonHelicopterMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: Robinson Helicopter First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Interest rate	9.63%		9.63%	9.63%	9.63%	9.63%
Maturity date	Jun. 30, 2028		Jun. 30, 2028	Jun. 30, 2028	Jun. 30, 2028	Jun. 30, 2028
Principal/Shares	$ 36,937
Investments, amortized cost	36,129
Investments at fair value	$ 36,199
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:RobinsonHelicopterMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: SAM First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	11.25%		11.25%	11.25%	11.25%	11.25%
Interest rate	11.25%		11.25%	11.25%	11.25%	11.25%
Maturity date	May 09, 2028		May 09, 2028	May 09, 2028	May 09, 2028	May 09, 2028
Principal/Shares	$ 32,500
Investments, amortized cost	32,213
Investments at fair value	$ 32,175
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SAMMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building		Construction and Building	Construction and Building	Construction and Building	Construction and Building
Investment, Identifier [Axis]: Saltoun First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	10.50%		10.50%	10.50%	10.50%	10.50%
Interest rate	10.50%		10.50%	10.50%	10.50%	10.50%
Maturity date	Apr. 11, 2028		Apr. 11, 2028	Apr. 11, 2028	Apr. 11, 2028	Apr. 11, 2028
Principal/Shares	$ 4,726
Investments, amortized cost	4,726
Investments at fair value	$ 4,584
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Saltoun [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Identifier [Axis]: Saltoun First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	10.50%		10.50%	10.50%	10.50%	10.50%
Interest rate	10.50%		10.50%	10.50%	10.50%	10.50%
Maturity date	Apr. 11, 2028		Apr. 11, 2028	Apr. 11, 2028	Apr. 11, 2028	Apr. 11, 2028
Principal/Shares	$ 1,352
Investments, amortized cost	1,352
Investments at fair value	$ 881
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Saltoun [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Identifier [Axis]: Saturn Purchaser Corp. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.60%		5.60%	5.60%	5.60%	5.60%
Interest rate	8.54%		8.54%	8.54%	8.54%	8.54%
Maturity date	Jul. 22, 2029		Jul. 22, 2029	Jul. 22, 2029	Jul. 22, 2029	Jul. 22, 2029
Principal/Shares	$ 56,867
Investments, amortized cost	56,303
Investments at fair value	$ 56,299
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Saturn Purchaser Corp [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Saturn Purchaser Corp. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.60%		5.60%	5.60%	5.60%	5.60%
Interest rate	8.62%		8.62%	8.62%	8.62%	8.62%
Maturity date	Jul. 22, 2029		Jul. 22, 2029	Jul. 22, 2029	Jul. 22, 2029	Jul. 22, 2029
Principal/Shares	$ 651
Investments, amortized cost	604
Investments at fair value	$ 602
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Saturn Purchaser Corp [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Service Master Equity Interest
Investments
Principal/Shares	$ 350
Investments, amortized cost	350	$ 327
Investments at fair value	$ 397	$ 353
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ServiceMasterMember	bcsf:ServiceMasterMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Identifier [Axis]: Service Master First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Interest rate	10.42%	8.50%	10.42%	10.42%	10.42%	10.42%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Maturity date	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027
Principal/Shares	$ 929	$ 939
Investments, amortized cost	914	921
Investments at fair value	$ 929	$ 939
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ServiceMasterMember	bcsf:ServiceMasterMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Service Master First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Interest rate	11.10%	8.50%	11.10%	11.10%	11.10%	11.10%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Maturity date	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027
Principal/Shares	$ 2,430	$ 1,260
Investments, amortized cost	2,357	1,176
Investments at fair value	$ 2,430	$ 1,260
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ServiceMasterMember	bcsf:ServiceMasterMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Service Master First Lien Senior Secured Loan Two
Investments
Spread Above Index (as a percent)	8.50%		8.50%	8.50%	8.50%	8.50%
Interest rate	11.53%		11.53%	11.53%	11.53%	11.53%
Maturity date	Aug. 16, 2027		Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027	Aug. 16, 2027
Principal/Shares	$ 22,000
Investments, amortized cost	22,000
Investments at fair value	$ 22,000
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ServiceMasterMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building		Construction and Building	Construction and Building	Construction and Building	Construction and Building
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Smartronix First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	10.17%		10.17%	10.17%	10.17%	10.17%
Maturity date	Nov. 23, 2027		Nov. 23, 2027	Nov. 23, 2027	Nov. 23, 2027	Nov. 23, 2027
Principal/Shares	$ 12,668
Investments, amortized cost	12,441
Investments at fair value	$ 12,351
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SmartronixMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Smartronix First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Nov. 23, 2027		Nov. 23, 2027	Nov. 23, 2027	Nov. 23, 2027	Nov. 23, 2027
Investments at fair value	$ (158)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SmartronixMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Smartronix RC First Lien Senior Secured Loan - Revolver
Investments
Maturity date		Nov. 23, 2028					Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028
Investments at fair value		$ (126)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:SmartronixRCMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Smartronix T/L First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		7.00%					7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date		Nov. 23, 2028					Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028	Nov. 23, 2028
Principal/Shares		$ 36,991
Investments, amortized cost		36,260
Investments at fair value		$ 36,251
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:SmartronixTLMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Solaray, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.50%	5.75%	5.75%	5.75%	5.75%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.40%	6.50%	9.40%	9.40%	9.40%	9.40%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023
Principal/Shares	$ 30,762	$ 41,729
Investments, amortized cost	30,762	41,729
Investments at fair value	$ 30,608	$ 41,729
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Solaray L L C [Member]	Solaray L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Solaray, LLC First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.75%	5.50%	5.75%	5.75%	5.75%	5.75%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.40%	6.50%	9.40%	9.40%	9.40%	9.40%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023
Principal/Shares	$ 14,202	$ 14,276
Investments, amortized cost	14,202	14,276
Investments at fair value	$ 14,131	$ 14,276
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Solaray L L C [Member]	Solaray L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Solaray, LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	3.55%	4.50%	3.55%	3.55%	3.55%	3.55%	4.50%	4.50%	4.50%	4.50%	4.50%	4.50%
Interest rate	8.16%	5.50%	8.16%	8.16%	8.16%	8.16%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Maturity date	Sep. 09, 2023	Sep. 09, 2022	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2023	Sep. 09, 2022	Sep. 09, 2022	Sep. 09, 2022	Sep. 09, 2022	Sep. 09, 2022	Sep. 09, 2022
Principal/Shares	$ 5,950	$ 907
Investments, amortized cost	5,950	895
Investments at fair value	$ 5,950	$ 907
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Solaray L L C [Member]	Solaray L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Spring Finco BV, First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	8.07%		8.07%	8.07%	8.07%	8.07%
Maturity date	Jul. 15, 2029		Jul. 15, 2029	Jul. 15, 2029	Jul. 15, 2029	Jul. 15, 2029
Principal/Shares	$ 49,343
Investments, amortized cost	5,160
Investments at fair value	$ 4,646
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Spring Finco BV [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Spring Finco BV, First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Jul. 15, 2029		Jul. 15, 2029	Jul. 15, 2029	Jul. 15, 2029	Jul. 15, 2029
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Spring Finco BV [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: Stanton Carpet Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Interest rate	12.75%	10.00%	12.75%	12.75%	12.75%	12.75%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Principal/Shares	$ 11,434	$ 19,664
Investments, amortized cost	11,229	19,277
Investments at fair value	$ 11,434	$ 19,271
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:StantonCarpetMember	bcsf:StantonCarpetMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: SumUp Holdings Luxembourg S.a.r.l. First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Interest rate	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026
Principal/Shares | €				€ 6,650				€ 6,650
Investments, amortized cost	$ 7,945							7,939
Investments at fair value	$ 6,519							€ 7,561
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SumUpHoldingsLuxembourgSarlMember	bcsf:SumUpHoldingsLuxembourgSarlMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: SumUp Holdings Luxembourg S.a.r.l. First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Interest rate	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026	Feb. 17, 2026
Principal/Shares				€ 155					£ 10,055
Investments, amortized cost	$ 180								11,700
Investments at fair value	$ 152								£ 11,432
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SumUpHoldingsLuxembourgSarlMember	bcsf:SumUpHoldingsLuxembourgSarlMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember	London Interbank Offered Rate (LIBOR) [Member]	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: SunMed Group Holdings, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	8.82%	6.50%	8.82%	8.82%	8.82%	8.82%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jun. 16, 2027	Jun. 16, 2028	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028
Principal/Shares	$ 590	$ 18,510
Investments, amortized cost	573	18,204
Investments at fair value	$ 550	$ 18,510
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SunMedGroupHoldingsLLCMember	bcsf:SunMedGroupHoldingsLLCMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: SunMed Group Holdings, LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%	6.50%	9.42%	9.42%	9.42%	9.42%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Jun. 16, 2028	Jun. 16, 2027	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2027	Jun. 16, 2027
Principal/Shares	$ 8,716	$ 197
Investments, amortized cost	8,585	177
Investments at fair value	$ 8,433	$ 197
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SunMedGroupHoldingsLLCMember	bcsf:SunMedGroupHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Superna Inc. Equity Interest
Investments
Principal/Shares	$ 1,463
Investments, amortized cost	1,463
Investments at fair value	$ 1,514
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Superna Inc [Member]
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Superna Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Interest rate	9.52%		9.52%	9.52%	9.52%	9.52%
Maturity date	Mar. 06, 2028		Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028
Principal/Shares	$ 14,958
Investments, amortized cost	14,675
Investments at fair value	$ 14,808
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Superna Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Superna Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Mar. 06, 2028		Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028
Investments at fair value	$ (26)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Superna Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Superna Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Mar. 06, 2028		Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028
Investments at fair value	$ (26)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Superna Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Surrey Bidco Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%	7.00%	6.00%	6.00%	6.00%	6.00%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Interest rate	7.97%	7.50%	7.97%	7.97%	7.97%	7.97%	7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026	May 11, 2026
Principal/Shares | £					£ 54				£ 50
Investments, amortized cost	$ 67								62
Investments at fair value	$ 52								£ 60
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:SurreyBidcoLimitedMember	bcsf:SurreyBidcoLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:SterlingOvernightInterbankAverageRateMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember	bcsf:BritishPoundSterlingLondonInterbankOfferedRateLiborMember
Investment, Identifier [Axis]: Swoogo LLC First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026
Investments at fair value	$ (22)	$ (25)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Swoogo L L C [Member]	Swoogo L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Swoogo LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%	8.00%
Interest rate	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%	9.00%
Maturity date	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026	Dec. 09, 2026
Principal/Shares	$ 2,330	$ 2,330
Investments, amortized cost	2,290	2,284
Investments at fair value	$ 2,289	$ 2,283
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Swoogo L L C [Member]	Swoogo L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TA/Weg Holdings First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	6.00%	5.75%	6.00%	6.00%	6.00%	6.00%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	7.67%	6.75%	7.67%	7.67%	7.67%	7.67%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Oct. 02, 2025	Oct. 02, 2027	Oct. 02, 2025	Oct. 02, 2025	Oct. 02, 2025	Oct. 02, 2025	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027
Principal/Shares	$ 2,379	$ 9,495
Investments, amortized cost	2,369	9,495
Investments at fair value	$ 2,379	$ 9,495
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:TAWegHoldingsMember	bcsf:TAWegHoldingsMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TA/Weg Holdings First Lien Senior Secured Loan - Delayed Draw 2
Investments
Spread Above Index (as a percent)	6.00%	5.75%	6.00%	6.00%	6.00%	6.00%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate	9.41%	6.75%	9.41%	9.41%	9.41%	9.41%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date	Oct. 02, 2025	Oct. 02, 2027	Oct. 02, 2025	Oct. 02, 2025	Oct. 02, 2025	Oct. 02, 2025	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027	Oct. 02, 2027
Principal/Shares	$ 9,423	$ 2,392
Investments, amortized cost	9,423	2,381
Investments at fair value	$ 9,423	$ 2,392
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:TAWegHoldingsMember	bcsf:TAWegHoldingsMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TCFIII Owl Finance, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	12.00%		12.00%	12.00%	12.00%	12.00%
Interest rate	12.00%		12.00%	12.00%	12.00%	12.00%
Maturity date	Jan. 30, 2027		Jan. 30, 2027	Jan. 30, 2027	Jan. 30, 2027	Jan. 30, 2027
Principal/Shares	$ 4,697
Investments, amortized cost	4,636
Investments at fair value	$ 4,603
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:TCFIIIOwlFinanceLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Capital Equipment Sector [Member]		Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Identifier [Axis]: TEI Holdings Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	7.00%	5.75%	5.75%	5.75%	5.75%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Interest rate	8.87%	8.25%	8.87%	8.87%	8.87%	8.87%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%
Maturity date	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Principal/Shares	$ 38,475	$ 48,720
Investments, amortized cost	38,283	48,350
Investments at fair value	$ 38,475	$ 48,720
PIK		(1.25%)					(1.25%)	(1.25%)	(1.25%)	(1.25%)	(1.25%)	(1.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T E I Holdings Inc [Member]	T E I Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TEI Holdings Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		6.00%					6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate		7.00%					7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025	Dec. 23, 2025
Principal/Shares		$ 458
Investments, amortized cost		412
Investments at fair value	$ 5	$ 458
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T E I Holdings Inc [Member]	T E I Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TGI Sport Bidco Pty Ltd First Lien Senior Secured Loan - Revolver
Investments
Maturity date		Apr. 30, 2027					Apr. 30, 2027	Apr. 30, 2027	Apr. 30, 2027	Apr. 30, 2027	Apr. 30, 2027	Apr. 30, 2027
Investments at fair value							$ (151)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		T G I Sport Bidco Pty Ltd [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Media: Advertising, Printing & Publishing					Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Identifier [Axis]: TGI Sport Bidco Pty Ltd First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	7.00%		7.00%	7.00%	7.00%	7.00%
Interest rate	10.60%		10.60%	10.60%	10.60%	10.60%
Maturity date	Apr. 30, 2026		Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares			$ 4,166
Investments, amortized cost	$ 2,720
Investments at fair value	$ 2,520
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T G I Sport Bidco Pty Ltd [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Advertising, Printing & Publishing		Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TGI Sport Bidco Pty Ltd First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	7.00%		7.00%	7.00%	7.00%	7.00%
Interest rate	8.50%		8.50%	8.50%	8.50%	8.50%
Maturity date	Apr. 30, 2026		Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares			$ 97
Investments, amortized cost	$ 75
Investments at fair value	$ 59
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T G I Sport Bidco Pty Ltd [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Media: Advertising, Printing & Publishing		Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:BankBillSwapBidRateMember		bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember
Investment, Identifier [Axis]: TGI Sport Bidco Pty Ltd First Lien Senior Secured Loan Bbsw
Investments
Spread Above Index (as a percent)		7.00%					7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Interest rate		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Maturity date		Apr. 30, 2026					Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares							$ 97
Investments, amortized cost							75
Investments at fair value							$ 67
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		T G I Sport Bidco Pty Ltd [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Media: Advertising, Printing & Publishing					Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing	Media: Advertising, Printing & Publishing
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:BankBillSwapBidRateMember					bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember
Investment, Identifier [Axis]: TLC Holdco LP Equity Interest
Investments
Principal/Shares	$ 1,281	$ 1,188
Investments, amortized cost	$ 1,221	1,186
Investments at fair value		$ 431
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:TLCHoldcoLPMember	bcsf:TLCHoldcoLPMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Identifier [Axis]: TLC Purchaser, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date		Oct. 13, 2025					Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025
Investments at fair value	$ (1,409)	$ (854)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T L C Purchaser, Inc [Member]	T L C Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Identifier [Axis]: TLC Purchaser, Inc.First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Interest rate	11.54%	7.25%	11.54%	11.54%	11.54%	11.54%	7.25%	7.25%	7.25%	7.25%	7.25%	7.25%
Maturity date		Oct. 13, 2025					Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025
Principal/Shares	$ 35,240	$ 41,066
Investments, amortized cost	34,579	40,511
Investments at fair value	$ 28,720	$ 36,137
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T L C Purchaser, Inc [Member]	T L C Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: TLC Purchaser, Inc.First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.25%	5.25%	6.25%	6.25%	6.25%	6.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate	9.37%	8.50%	9.37%	9.37%	9.37%	9.37%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Maturity date		Oct. 13, 2025					Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025
Principal/Shares	$ 7,693	$ 6,408
Investments, amortized cost	7,536	6,296
Investments at fair value	$ 5,932	$ 5,340
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	T L C Purchaser, Inc [Member]	T L C Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Tangent Technologies Acquisition, LLCSecond Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	8.75%		8.75%	8.75%	8.75%	8.75%
Interest rate	9.99%		9.99%	9.99%	9.99%	9.99%
Principal/Shares	$ 8,915
Investments, amortized cost	8,752
Investments at fair value	$ 8,915
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:TangentTechnologiesAcquisitionLLCMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]		Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: TecoStar Holdings, Inc. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Interest rate	11.31%	9.50%	11.31%	11.31%	11.31%	11.31%	9.50%	9.50%	9.50%	9.50%	9.50%	9.50%
Maturity date	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024	Nov. 01, 2024
Principal/Shares	$ 9,472	$ 9,472
Investments, amortized cost	9,381	9,354
Investments at fair value	$ 9,022	$ 8,951
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:TecoStarHoldingsIncMember	bcsf:TecoStarHoldingsIncMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Thrasio, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.00%		7.00%	7.00%	7.00%	7.00%
Interest rate	11.17%		11.17%	11.17%	11.17%	11.17%
Maturity date	Dec. 18, 2026		Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026
Principal/Shares	$ 8,506
Investments, amortized cost	8,320
Investments at fair value	$ 7,826
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Thrasio, LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		7.00%					7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Interest rate		8.00%					8.00%	8.00%	8.00%	8.00%	8.00%	8.00%
Maturity date		Dec. 18, 2026					Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026
Principal/Shares		$ 21,746
Investments, amortized cost		21,241
Investments at fair value		$ 21,746
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:ThrasioLLCMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Tidel Engineering, L.P. First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Mar. 01, 2024					Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024
Principal/Shares		$ 38,155
Investments, amortized cost		38,155
Investments at fair value		$ 38,155
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:TidelEngineeringLPMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Capital Equipment Sector [Member]					Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Tidel Engineering, L.P. First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Mar. 01, 2024					Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024	Mar. 01, 2024
Principal/Shares		$ 6,337
Investments, amortized cost		6,274
Investments at fair value		$ 6,336
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:TidelEngineeringLPMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoan2Member					bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member	bcsf:FirstLienSeniorSecuredLoan2Member
Investment, Industry Sector [Extensible Enumeration]		Capital Equipment Sector [Member]					Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]	Capital Equipment Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Titan Cloud Software, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.60%		6.60%	6.60%	6.60%	6.60%
Interest rate	9.63%		9.63%	9.63%	9.63%	9.63%
Maturity date	Sep. 07, 2029		Sep. 07, 2029	Sep. 07, 2029	Sep. 07, 2029	Sep. 07, 2029
Principal/Shares | €				€ 25,714
Investments, amortized cost	$ 25,457
Investments at fair value	$ 25,457
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Titan Cloud Software, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Titan Cloud Software, Inc First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Sep. 07, 2029		Sep. 07, 2029	Sep. 07, 2029	Sep. 07, 2029	Sep. 07, 2029
Investments at fair value	$ (114)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Titan Cloud Software, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Identifier [Axis]: Titan Cloud Software, Inc First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Sep. 07, 2028		Sep. 07, 2028	Sep. 07, 2028	Sep. 07, 2028	Sep. 07, 2028
Investments at fair value	$ (57)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Titan Cloud Software, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Environmental Industries Sector [Member]		Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]	Environmental Industries Sector [Member]
Investment, Identifier [Axis]: Toro Private Investments II, LP Equity Interest
Investments
Principal/Shares	$ 3,090	$ 3,090
Investments, amortized cost	3,090	3,090
Investments at fair value	$ 1,173	$ 1,353
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ToroPrivateInvestmentsIILPMember	bcsf:ToroPrivateInvestmentsIILPMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Equity Securities [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]	Equity Securities [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Toro Private Investments II, LP First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	5.00%	6.75%	5.00%	5.00%	5.00%	5.00%	6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Interest rate	10.42%	6.90%	10.42%	10.42%	10.42%	10.42%	6.90%	6.90%	6.90%	6.90%	6.90%	6.90%
Maturity date	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026	May 29, 2026
Principal/Shares	$ 6,744	$ 6,706
Investments, amortized cost	5,182	4,846
Investments at fair value	$ 4,794	$ 5,603
PIK	(1.75%)		(1.75%)	(1.75%)	(1.75%)	(1.75%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ToroPrivateInvestmentsIILPMember	bcsf:ToroPrivateInvestmentsIILPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Toro Private Investments ll, LP First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%
Interest rate	12.42%	9.75%	12.42%	12.42%	12.42%	12.42%	9.75%	9.75%	9.75%	9.75%	9.75%	9.75%
Maturity date	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025	Feb. 28, 2025
Principal/Shares	$ 394	$ 366
Investments, amortized cost	391	363
Investments at fair value	$ 391	$ 377
PIK	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)	(7.25%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ToroPrivateInvestmentsIILPMember	bcsf:ToroPrivateInvestmentsIILPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Consumer [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]	Transportation Consumer Non Controlled Non Affiliate [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Utimaco, Inc. Equity Interest
Investments
Principal/Shares	$ 1
Investments, amortized cost	2,123
Investments at fair value	$ 2,006
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:UtimacoIncMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Utimaco, Inc. First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	6.58%		6.58%	6.58%	6.58%	6.58%
Maturity date	May 13, 2029		May 13, 2029	May 13, 2029	May 13, 2029	May 13, 2029
Principal/Shares	$ 92
Investments, amortized cost	100
Investments at fair value	$ 91
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:UtimacoIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: Utimaco, Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		4.00%					4.00%	4.00%	4.00%	4.00%	4.00%	4.00%
Interest rate		4.10%					4.10%	4.10%	4.10%	4.10%	4.10%	4.10%
Maturity date		Aug. 09, 2027					Aug. 09, 2027	Aug. 09, 2027	Aug. 09, 2027	Aug. 09, 2027	Aug. 09, 2027	Aug. 09, 2027
Principal/Shares		$ 148
Investments, amortized cost		146
Investments at fair value		$ 148
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:UtimacoIncMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Utimaco, Inc. First Lien Senior Secured Loan Sofr 1
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	8.83%		8.83%	8.83%	8.83%	8.83%
Maturity date	May 13, 2029		May 13, 2029	May 13, 2029	May 13, 2029	May 13, 2029
Principal/Shares	$ 128
Investments, amortized cost	127
Investments at fair value	$ 128
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:UtimacoIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Utimaco, Inc. First Lien Senior Secured Loan Sofr 2
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	8.83%		8.83%	8.83%	8.83%	8.83%
Maturity date	May 13, 2029		May 13, 2029	May 13, 2029	May 13, 2029	May 13, 2029
Principal/Shares	$ 262
Investments, amortized cost	259
Investments at fair value	$ 262
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:UtimacoIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Investment, Identifier [Axis]: Utimaco, Inc. Preferred Equity
Investments
Principal/Shares	$ 1
Investments, amortized cost	2,123
Investments at fair value	$ 2,006
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:UtimacoIncMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: V Global Holdings LLCFirst Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%	6.00%	5.75%	5.75%	5.75%	5.75%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	8.99%	7.00%	8.99%	8.99%	8.99%	8.99%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027
Principal/Shares	$ 5,876	$ 24,813
Investments, amortized cost	5,795	24,242
Investments at fair value	$ 5,772	$ 24,813
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	V Global Holdings L L C [Member]	V Global Holdings L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: V Global Holdings LLCFirst Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%	5.00%	5.75%	5.75%	5.75%	5.75%	5.00%	5.00%	5.00%	5.00%	5.00%	5.00%
Interest rate	8.45%	8.25%	8.45%	8.45%	8.45%	8.45%	8.25%	8.25%	8.25%	8.25%	8.25%	8.25%
Maturity date	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025	Dec. 22, 2025
Principal/Shares	$ 1,351	$ 2,050
Investments, amortized cost	1,192	1,893
Investments at fair value	$ 1,182	$ 2,050
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	V Global Holdings L L C [Member]	V Global Holdings L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	us-gaap:PrimeRateMember	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember
Investment, Identifier [Axis]: V Global Holdings Llc First Lien Senior Secured Loan Two
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	6.50%		6.50%	6.50%	6.50%	6.50%
Maturity date	Dec. 22, 2027		Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027
Principal/Shares | €				€ 100
Investments, amortized cost	$ 103
Investments at fair value	$ 97
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	V Global Holdings L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Chemicals, Plastics & Rubber		Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: VPARK BIDCO AB First Lien Senior Secured Loan Cibor
Investments
Spread Above Index (as a percent)	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%
Interest rate	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Maturity date	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025
Principal/Shares				€ 570							kr 570
Investments, amortized cost	$ 92										92
Investments at fair value	$ 75										kr 87
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:VPARKBIDCOABMember	bcsf:VPARKBIDCOABMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:CopenhagenInterbankOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CopenhagenInterbankOfferedRateMember	bcsf:CopenhagenInterbankOfferedRateMember	bcsf:CopenhagenInterbankOfferedRateMember	bcsf:CopenhagenInterbankOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember	bcsf:CanadianDollarOfferedRateMember
Investment, Identifier [Axis]: VPARK BIDCO AB First Lien Senior Secured Loan Nibor
Investments
Spread Above Index (as a percent)	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%	4.00%
Interest rate	6.60%	4.75%	6.60%	6.60%	6.60%	6.60%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Maturity date	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025	Mar. 10, 2025
Principal/Shares	$ 740											kr 740
Investments, amortized cost	93											93
Investments at fair value	$ 68											kr 84
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:VPARKBIDCOABMember	bcsf:VPARKBIDCOABMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember	bcsf:NorwegianInterbankOfferedRateMember
Investment, Identifier [Axis]: Ventiv Holdco, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Sep. 03, 2025		Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025
Investments at fair value	$ (68)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Ventiv Holdco, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Ventiv Holdco, Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%	6.50%	9.17%	9.17%	9.17%	9.17%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025
Principal/Shares	$ 13,807	$ 23,812
Investments, amortized cost	13,693	23,576
Investments at fair value	$ 13,531	$ 23,812
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Ventiv Holdco, Inc [Member]	Ventiv Holdco, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Ventiv Topco, Inc. Equity Interest
Investments
Principal/Shares	$ 28	$ 28
Investments, amortized cost	2,833	2,833
Investments at fair value	$ 2,121	$ 2,755
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:VentivTopcoIncMember	bcsf:VentivTopcoIncMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: Ventiv Topco, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date		Sep. 03, 2025					Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:VentivTopcoIncMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		High Tech Industries [Member]					High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Identifier [Axis]: WCI Gigawatt Purchaser DD T/L First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Nov. 19, 2027					Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Principal/Shares		$ 3,182
Investments, amortized cost		3,076
Investments at fair value		$ 3,074
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		W C I Gigawatt Purchaser D D T L [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WCI Gigawatt Purchaser First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.73%		8.73%	8.73%	8.73%	8.73%
Maturity date	Nov. 19, 2027		Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Principal/Shares	$ 1,447
Investments, amortized cost	1,446
Investments at fair value	$ 1,415
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCIGigawattPurchaserMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WCI Gigawatt Purchaser First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.73%		8.73%	8.73%	8.73%	8.73%
Maturity date	Nov. 19, 2027		Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Principal/Shares	$ 3,195
Investments, amortized cost	3,101
Investments at fair value	$ 3,086
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCIGigawattPurchaserMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WCI Gigawatt Purchaser First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.51%		8.51%	8.51%	8.51%	8.51%
Maturity date	Nov. 19, 2027		Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Principal/Shares	$ 965
Investments, amortized cost	903
Investments at fair value	$ 893
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCIGigawattPurchaserMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WCI Gigawatt Purchaser R/C First Lien Senior Secured Loan - Revolver
Investments
Maturity date		Nov. 19, 2027					Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Investments at fair value		$ (72)
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:WCIGigawattPurchaserRCMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: WCI Gigawatt Purchaser T/L First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Nov. 19, 2027					Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Principal/Shares		$ 22,304
Investments, amortized cost		21,809
Investments at fair value		$ 21,802
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:WCIGigawattPurchaserTLMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WCI-HSG HOLDCO, LLC Preferred Equity
Investments
Principal/Shares	$ 675	$ 675
Investments, amortized cost	675	675
Investments at fair value	$ 2,217	$ 1,993
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCI-HSGHOLDCOLLCMember	bcsf:WCI-HSGHOLDCOLLCMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Identifier [Axis]: WCI-HSG Purchaser, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%	4.75%	4.50%	4.50%	4.50%	4.50%	4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate	7.62%	5.75%	7.62%	7.62%	7.62%	7.62%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025
Principal/Shares	$ 8,644	$ 17,422
Investments, amortized cost	8,591	17,285
Investments at fair value	$ 8,644	$ 17,422
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCI-HSGPurchaserIncMember	bcsf:WCI-HSGPurchaserIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WCI-HSG Purchaser, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		4.75%					4.75%	4.75%	4.75%	4.75%	4.75%	4.75%
Interest rate		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Maturity date	Feb. 22, 2025	Feb. 24, 2025	Feb. 22, 2025	Feb. 22, 2025	Feb. 22, 2025	Feb. 22, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025
Principal/Shares		$ 1,209
Investments, amortized cost		1,190
Investments at fair value		$ 1,209
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCI-HSGPurchaserIncMember	bcsf:WCI-HSGPurchaserIncMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WP CPP Holdings, LLC Senior Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%	7.75%
Interest rate	10.56%	8.75%	10.56%	10.56%	10.56%	10.56%	8.75%	8.75%	8.75%	8.75%	8.75%	8.75%
Maturity date	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026	Apr. 30, 2026
Principal/Shares	$ 11,724	$ 11,724
Investments, amortized cost	11,658	11,646
Investments at fair value	$ 10,815	$ 11,495
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WPCPPHoldingsLLCMember	bcsf:WPCPPHoldingsLLCMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WSP Initial Term Loan First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.37%		9.37%	9.37%	9.37%	9.37%
Maturity date	Apr. 27, 2027	Apr. 27, 2023	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2023	Apr. 27, 2023	Apr. 27, 2023	Apr. 27, 2023	Apr. 27, 2023	Apr. 27, 2023
Principal/Shares	$ 6,018
Investments, amortized cost	5,916
Investments at fair value	$ 5,626	$ (31)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	WSP Initial Term Loan	WSP Initial Term Loan
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WSP Initial Term Loan First Lien Senior Secured Loan - Delayed Draw
Investments
Maturity date	Apr. 27, 2027		Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027
Investments at fair value	$ (117)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	WSP Initial Term Loan
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Wholesale Sector [Member]		Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]
Investment, Identifier [Axis]: WSP Initial Term Loan First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		6.25%					6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Interest rate		7.25%					7.25%	7.25%	7.25%	7.25%	7.25%	7.25%
Maturity date		Apr. 27, 2027					Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027
Principal/Shares		$ 12,251
Investments, amortized cost		12,017
Investments at fair value		$ 12,037
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		WSP Initial Term Loan
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Consumer Goods Wholesale Sector [Member]					Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WSP LP Interest Equity Interest
Investments
Principal/Shares	$ 2,898	$ 2,898
Investments, amortized cost	2,898	2,898
Investments at fair value	$ 1,559	$ 2,829
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WSPLPInterestMember	bcsf:WSPLPInterestMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]
Investment, Identifier [Axis]: WSP Revolving Loan First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	6.25%		6.25%	6.25%	6.25%	6.25%
Maturity date	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027
Principal/Shares	$ 47
Investments, amortized cost	40
Investments at fair value	$ 18	$ (8)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:WSPLPInterestMember	WSP Revolving Loan
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%	6.50%	9.17%	9.17%	9.17%	9.17%	6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026
Principal/Shares	$ 37,775	$ 44,452
Investments, amortized cost	37,341	43,847
Investments at fair value	$ 35,886	$ 44,452
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	WU Holdco, Inc.	WU Holdco, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%		9.17%	9.17%	9.17%	9.17%
Maturity date	Mar. 26, 2026		Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026
Principal/Shares	$ 1,704
Investments, amortized cost	1,677
Investments at fair value	$ 1,619
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	WU Holdco, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		5.72%					5.72%	5.72%	5.72%	5.72%	5.72%	5.72%
Maturity date		Mar. 26, 2025					Mar. 26, 2025	Mar. 26, 2025	Mar. 26, 2025	Mar. 26, 2025	Mar. 26, 2025	Mar. 26, 2025
Principal/Shares		$ 1,690
Investments, amortized cost		1,656
Investments at fair value		$ 1,690
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		WU Holdco, Inc.
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Consumer Goods Non Durable Sector [Member]					Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan - Revolver Libor
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.14%		9.14%	9.14%	9.14%	9.14%
Maturity date	Mar. 26, 2025		Mar. 26, 2025	Mar. 26, 2025	Mar. 26, 2025	Mar. 26, 2025
Principal/Shares	$ 2,930
Investments, amortized cost	2,904
Investments at fair value	$ 2,648
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	WU Holdco, Inc.
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		5.50%					5.50%	5.50%	5.50%	5.50%	5.50%	5.50%
Interest rate		6.50%					6.50%	6.50%	6.50%	6.50%	6.50%	6.50%
Maturity date		Mar. 26, 2026					Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026
Principal/Shares		$ 6,594
Investments, amortized cost		6,534
Investments at fair value		$ 6,594
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		WU Holdco, Inc.
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Consumer Goods Non Durable Sector [Member]					Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan Libor One
Investments
Maturity date		Mar. 26, 2026					Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		WU Holdco, Inc.
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Consumer Goods Non Durable Sector [Member]					Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Identifier [Axis]: Walker Edison First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	12.42%		12.42%	12.42%	12.42%	12.42%
Maturity date	Mar. 31, 2027		Mar. 31, 2027	Mar. 31, 2027	Mar. 31, 2027	Mar. 31, 2027
Principal/Shares	$ 20,912
Investments, amortized cost	20,736
Investments at fair value	$ 14,220
PIK	(3.00%)		(3.00%)	(3.00%)	(3.00%)	(3.00%)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	New Look Vision Group [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Walker Edison Initial Term Loan First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		9.75%					9.75%	9.75%	9.75%	9.75%	9.75%	9.75%
Maturity date		Aug. 05, 2027					Aug. 05, 2027	Aug. 05, 2027	Aug. 05, 2027	Aug. 05, 2027	Aug. 05, 2027	Aug. 05, 2027
Principal/Shares		$ 20,447
Investments, amortized cost		20,248
Investments at fair value		$ 19,627
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:WalkerEdisonInitialTermLoanMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Retail Sector					Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Whitcraft LLC First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023
Principal/Shares	$ 28,760
Investments, amortized cost	28,705
Investments at fair value	$ 27,466	$ (59)
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Whitcraft L L C [Member]	Whitcraft L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Whitcraft LLC Senior Secured Loan First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%	6.00%	5.00%	5.00%	5.00%	5.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	11.25%	7.00%	11.25%	11.25%	11.25%	11.25%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023
Principal/Shares	$ 254	$ 39,775
Investments, amortized cost	251	39,594
Investments at fair value	$ 172	$ 38,482
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	Whitcraft L L C [Member]	Whitcraft L L C [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	First Lien Senior Secured Loan [Member]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	us-gaap:PrimeRateMember	London Interbank Offered Rate (LIBOR) [Member]	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	us-gaap:PrimeRateMember	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: World Insurance First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Apr. 01, 2026					Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026
Principal/Shares		$ 3,144
Investments, amortized cost		3,088
Investments at fair value		$ 3,121
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		World Insurance [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: World Insurance First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Apr. 01, 2026					Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026
Principal/Shares		$ 8,358
Investments, amortized cost		8,285
Investments at fair value		$ 8,296
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		World Insurance [Member]
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan Delayed Draw [Member]					First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: World Insurance First Lien Senior Secured Loan - Delayed Draw Libor
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.30%		9.30%	9.30%	9.30%	9.30%
Maturity date	Apr. 01, 2026		Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026
Principal/Shares	$ 8,295
Investments, amortized cost	8,236
Investments at fair value	$ 8,295
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	World Insurance [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: World Insurance First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)		5.75%					5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Interest rate		6.75%					6.75%	6.75%	6.75%	6.75%	6.75%	6.75%
Maturity date		Apr. 01, 2026					Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026
Principal/Shares		$ 70
Investments, amortized cost		54
Investments at fair value		$ 63
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		World Insurance [Member]
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Fire Insurance					Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: World Insurance First Lien Senior Secured Loan - Revolver Libor
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.30%		9.30%	9.30%	9.30%	9.30%
Maturity date	Apr. 01, 2026		Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026
Principal/Shares	$ 256
Investments, amortized cost	243
Investments at fair value	$ 256
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	World Insurance [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: World Insurance First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.30%		9.30%	9.30%	9.30%	9.30%
Maturity date	Apr. 01, 2026		Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026	Apr. 01, 2026
Principal/Shares	$ 3,122
Investments, amortized cost	3,075
Investments at fair value	$ 3,122
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	World Insurance [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Insurance		Fire Insurance	Fire Insurance	Fire Insurance	Fire Insurance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: YLG Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%	5.25%
Interest rate	7.10%	6.25%	7.10%	7.10%	7.10%	7.10%	6.25%	6.25%	6.25%	6.25%	6.25%	6.25%
Maturity date	Oct. 31, 2025		Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025
Principal/Shares	$ 27,221	$ 38,086
Investments, amortized cost	27,124	37,900
Investments at fair value	$ 27,153	$ 38,086
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	YLG Holdings, Inc.	YLG Holdings, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: YLG Holdings, Inc. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	5.00%	6.00%	5.00%	5.00%	5.00%	5.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	7.08%	7.00%	7.08%	7.08%	7.08%	7.08%	7.00%	7.00%	7.00%	7.00%	7.00%	7.00%
Maturity date	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025
Principal/Shares	$ 5,022	$ 5,060
Investments, amortized cost	5,017	5,055
Investments at fair value	$ 5,009	$ 5,060
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	YLG Holdings, Inc.	YLG Holdings, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: YLG Holdings, Inc. First Lien Senior Secured Loan - Revolver
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	7.93%		7.93%	7.93%	7.93%	7.93%
Maturity date	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025
Principal/Shares	$ 855
Investments, amortized cost	811
Investments at fair value	$ 833
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	YLG Holdings, Inc.	YLG Holdings, Inc.
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	Construction and Building	Construction and Building	Construction and Building	Construction and Building	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: Zeppelin BidCo Pty Limited First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%	6.00%	5.00%	5.00%	5.00%	5.00%	6.00%	6.00%	6.00%	6.00%	6.00%	6.00%
Interest rate	7.12%	5.12%	7.12%	7.12%	7.12%	7.12%	5.12%	5.12%	5.12%	5.12%	5.12%	5.12%
Maturity date	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024	Jun. 28, 2024
Principal/Shares			$ 206				$ 206
Investments, amortized cost	$ 142						142
Investments at fair value	$ 131						$ 150
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:ZeppelinBidCoPtyLimitedMember	bcsf:ZeppelinBidCoPtyLimitedMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember	bcsf:BankBillSwapBidRateMember
Investment, Identifier [Axis]: iBanFirst Facility B First Lien Senior Secured Loan Euibor
Investments
Spread Above Index (as a percent)		8.50%					8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Interest rate		10.00%					10.00%	10.00%	10.00%	10.00%	10.00%	10.00%
Maturity date		Jul. 13, 2028					Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028
Principal/Shares | €								€ 102
Investments, amortized cost | €								128
Investments at fair value | €								€ 116
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:iBanFirstFacilityBMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:EuroInterbankOfferRateMember					bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: iBanFirst Facility Preferred Equity
Investments
Principal/Shares | €				€ 7,112
Investments, amortized cost	$ 8,136
Investments at fair value	$ 9,252
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:iBanFirstFacilityMember
Investment, Type [Extensible Enumeration]	Preferred Stock [Member]		Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: iBanFirst Facility Series A Preferred Units Preferred Equity
Investments
Principal/Shares		$ 5,080
Investments, amortized cost		5,996
Investments at fair value		$ 6,290
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:iBanFirstFacilitySeriesAPreferredUnitsMember
Investment, Type [Extensible Enumeration]		Preferred Stock [Member]					Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: iBanFirst First Lien Senior Secured Loan 1
Investments
Spread Above Index (as a percent)	8.50%		8.50%	8.50%	8.50%	8.50%
Interest rate	10.00%		10.00%	10.00%	10.00%	10.00%
Maturity date	Jul. 13, 2028		Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028
Principal/Shares	$ 2,748
Investments, amortized cost	2,817
Investments at fair value	$ 2,694
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:iBanFirstMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: iBanFirst First Lien Senior Secured Loan 2
Investments
Spread Above Index (as a percent)	10.00%		10.00%	10.00%	10.00%	10.00%
Interest rate	10.00%		10.00%	10.00%	10.00%	10.00%
Maturity date	Jul. 13, 2028		Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028
Principal/Shares | €				€ 80
Investments, amortized cost	$ 83
Investments at fair value	$ 78
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:iBanFirstMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	bcsf:EuroInterbankOfferRateMember		bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: iBanFirst First Lien Senior Secured Loan Euribor
Investments
Maturity date	Jul. 13, 2028		Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:iBanFirstMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: iBanFirst Revolving Facility First Lien Senior Secured Loan - Revolver Euibor
Investments
Spread Above Index (as a percent)		8.50%					8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Interest rate		8.50%					8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Maturity date		Jul. 13, 2028					Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028	Jul. 13, 2028
Principal/Shares | €								€ 2,030
Investments, amortized cost | €								2,244
Investments at fair value | €								€ 2,308
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:iBanFirstRevolvingFacilityMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		bcsf:EuroInterbankOfferRateMember					bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember	bcsf:EuroInterbankOfferRateMember
Investment, Identifier [Axis]: masLabor Equity Equity Interest
Investments
Principal/Shares		$ 345
Investments, amortized cost		345
Investments at fair value		$ 372
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:masLaborEquityMember
Investment, Type [Extensible Enumeration]		Common Stock [Member]					Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: masLabor Equity Interest
Investments
Principal/Shares	$ 345
Investments, amortized cost	345
Investments at fair value	$ 909
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:masLaborMember
Investment, Type [Extensible Enumeration]	Common Stock [Member]		Common Stock [Member]	Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: masLabor First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.50%		7.50%	7.50%	7.50%	7.50%
Interest rate	8.50%		8.50%	8.50%	8.50%	8.50%
Maturity date	Jul. 01, 2027		Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027
Principal/Shares | £					£ 8,513
Investments, amortized cost	$ 8,289
Investments at fair value	$ 8,513
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:masLaborMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Investment, Identifier [Axis]: masLabor First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Jul. 01, 2027		Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]	bcsf:masLaborMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: masLabor Revolver First Lien Senior Secured Loan - Revolver
Investments
Maturity date		Jul. 01, 2027					Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:masLaborRevolverMember
Investment, Type [Extensible Enumeration]		bcsf:FirstLienSeniorSecuredLoanRevolverMember					bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Identifier [Axis]: masLabor Term Loan Note First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)		7.50%					7.50%	7.50%	7.50%	7.50%	7.50%	7.50%
Interest rate		8.50%					8.50%	8.50%	8.50%	8.50%	8.50%	8.50%
Maturity date		Jul. 01, 2027					Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027	Jul. 01, 2027
Principal/Shares		$ 8,578
Investments, amortized cost		8,324
Investments at fair value		$ 8,578
Investment, Issuer Affiliation [Extensible Enumeration]		Investment, Unaffiliated Issuer [Member]					Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Investment, Issuer Name [Extensible Enumeration]		bcsf:masLaborTermLoanNoteMember
Investment, Type [Extensible Enumeration]		First Lien Senior Secured Loan [Member]					First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]		Services, Business					Services, Business	Services, Business	Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]		London Interbank Offered Rate (LIBOR) [Member]					London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Aerospace Sector [Member]
Investments
Investments, amortized cost	$ 398,665	$ 309,458
Investments at fair value	380,118	282,598
Aerospace and Defense Sector [Member]
Investments
Investments, amortized cost	287,223	109,341
Investments at fair value	$ 105,303	$ 90,029
% of Member's Equity	25.10%	8.20%	25.10%	25.10%	25.10%	25.10%	8.20%	8.20%	8.20%	8.20%	8.20%	8.20%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Automotive Sector [Member]
Investments
Investments, amortized cost	$ 78,189	$ 87,597
Investments at fair value	$ 78,215	$ 88,555
% of Member's Equity	7.10%	8.10%	7.10%	7.10%	7.10%	7.10%	8.10%	8.10%	8.10%	8.10%	8.10%	8.10%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Banking [Member]
Investments
Investments, amortized cost	$ 7,736	$ 18,370
Investments at fair value	$ 7,980	$ 18,690
% of Member's Equity	0.70%	1.70%	0.70%	0.70%	0.70%	0.70%	1.70%	1.70%	1.70%	1.70%	1.70%	1.70%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Banking Finance Insurance And Real Estate Sector [Member]
Investments
Investments, amortized cost	$ 150
Investments at fair value	$ 160
% of Member's Equity	0.00%		0.00%	0.00%	0.00%	0.00%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]		Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Chemicals, Plastics & Rubber
Investments
Investments, amortized cost	$ 14,177	$ 26,135
Investments at fair value	$ 14,065	$ 26,863
% of Member's Equity	1.30%	2.40%	1.30%	1.30%	1.30%	1.30%	2.40%	2.40%	2.40%	2.40%	2.40%	2.40%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Construction and Building
Investments
Investments, amortized cost	$ 117,017	$ 70,256
Investments at fair value	$ 113,634	$ 68,570
% of Member's Equity	10.40%	6.20%	10.40%	10.40%	10.40%	10.40%	6.20%	6.20%	6.20%	6.20%	6.20%	6.20%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Containers, Packaging and Glass
Investments
Investments, amortized cost	$ 16,372	$ 27,379
Investments at fair value	16,071	27,378
Energy: Oil and Gas
Investments
Investments, amortized cost	57,002	69,588
Investments at fair value	74,898	79,548
Fire Finance
Investments
Investments, amortized cost	49,741	24,245
Investments at fair value	$ 47,545	$ 24,452
% of Member's Equity	2.30%	2.20%	2.30%	2.30%	2.30%	2.30%	2.20%	2.20%	2.20%	2.20%	2.20%	2.20%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Fire Insurance
Investments
Investments, amortized cost	$ 64,944	$ 62,165
Investments at fair value	$ 62,954	$ 63,123
% of Member's Equity	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%	5.70%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Healthcare and Pharmaceuticals
Investments
Investments, amortized cost	$ 101,715	$ 102,116
Investments at fair value	99,633	100,771
High Tech Industries
Investments
Investments, amortized cost	220,512	182,811
Investments at fair value	217,497	183,069
Hotel, Gaming & Leisure
Investments
Investments, amortized cost	37,159	53,232
Investments at fair value	$ 36,068	$ 51,956
% of Member's Equity	3.30%	4.70%	3.30%	3.30%	3.30%	3.30%	4.70%	4.70%	4.70%	4.70%	4.70%	4.70%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Retail Sector
Investments
Investments, amortized cost	$ 60,350	$ 83,036
Investments at fair value	53,266	83,064
Services, Business
Investments
Investments, amortized cost	170,902	226,035
Investments at fair value	$ 163,918	$ 225,437
% of Member's Equity	15.00%	20.50%	15.00%	15.00%	15.00%	15.00%	20.50%	20.50%	20.50%	20.50%	20.50%	20.50%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Services, Consumer [Business]
Investments
Investments, amortized cost	$ 17,585	$ 40,467
Investments at fair value	$ 17,823	$ 41,236
% of Member's Equity	1.60%	3.70%	1.60%	1.60%	1.60%	1.60%	3.70%	3.70%	3.70%	3.70%	3.70%	3.70%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Telecommunications Sector [Member]
Investments
Investments, amortized cost	$ 46,415	$ 40,938
Investments at fair value	47,204	41,570
Wholesale
Investments
Investments, amortized cost	26,426	77,737
Investments at fair value	$ 27,640	$ 80,070
% of Member's Equity	2.50%	7.30%	2.50%	2.50%	2.50%	2.50%	7.30%	7.30%	7.30%	7.30%	7.30%	7.30%
Investment, Issuer Affiliation [Extensible Enumeration]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]	Investment, Unaffiliated Issuer [Member]
Bain Capital Senior Loan Program, LLC
Investments
Investments, amortized cost	$ 575,658
Investments at fair value	$ 570,584
% of Member's Equity	2.1653%		2.1653%	2.1653%	2.1653%	2.1653%
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: A R Logistics Inc. First Lien Senior Secured Loan
Investments
Interest rate	9.71%		9.71%	9.71%	9.71%	9.71%
Maturity date	May 05, 2025		May 05, 2025	May 05, 2025	May 05, 2025	May 05, 2025
Principal/Shares	$ 10,696
Investments, amortized cost	10,696
Investments at fair value	$ 10,696
Investment, Issuer Name [Extensible Enumeration]	bcsf:ARLogisticsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: AMI US Holdings Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.25%		5.25%	5.25%	5.25%	5.25%
Interest rate	7.81%		7.81%	7.81%	7.81%	7.81%
Maturity date	Apr. 01, 2025		Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025	Apr. 01, 2025
Principal/Shares	$ 8,926
Investments, amortized cost	8,926
Investments at fair value	$ 8,926
Investment, Issuer Name [Extensible Enumeration]	bcsf:AMIUSHoldingsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: AMI US Holdings Inc. First Lien Senior Secured Loan - Revolver Libor
Investments
Maturity date	Apr. 01, 2024		Apr. 01, 2024	Apr. 01, 2024	Apr. 01, 2024	Apr. 01, 2024
Investment, Issuer Name [Extensible Enumeration]	bcsf:AMIUSHoldingsIncMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: ASP-r-pac Acquisition Co LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	Dec. 29, 2027		Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027	Dec. 29, 2027
Principal/Shares	$ 23,109
Investments, amortized cost	22,873
Investments at fair value	$ 22,936
Investment, Issuer Name [Extensible Enumeration]	bcsf:ASP-r-pacAcquisitionCoLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Containers Packaging And Glass [Member]		Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Abracon Group Holding, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	7.86%		7.86%	7.86%	7.86%	7.86%
Maturity date	Jul. 06, 2028		Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028	Jul. 06, 2028
Principal/Shares	$ 12,000
Investments, amortized cost	11,764
Investments at fair value	$ 11,760
Investment, Issuer Name [Extensible Enumeration]	bcsf:AbraconGroupHoldingLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Wholesale		Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Aimbridge Acquisition Co., Inc. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.50%		7.50%	7.50%	7.50%	7.50%
Interest rate	10.06%		10.06%	10.06%	10.06%	10.06%
Maturity date	Feb. 01, 2027		Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027	Feb. 01, 2027
Principal/Shares	$ 6,000
Investments, amortized cost	5,580
Investments at fair value	$ 5,670
Investment, Issuer Name [Extensible Enumeration]	bcsf:AimbridgeAcquisitionCoIncMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan
Investments
Interest rate	7.88%		7.88%	7.88%	7.88%	7.88%
Maturity date	Dec. 23, 2026		Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Principal/Shares	$ 8,452
Investments, amortized cost	8,452
Investments at fair value	$ 8,452
Investment, Issuer Name [Extensible Enumeration]	bcsf:AllworthFinancialGroupLPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan - Delayed Draw
Investments
Interest rate	7.88%		7.88%	7.88%	7.88%	7.88%
Maturity date	Dec. 23, 2026		Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Principal/Shares	$ 2,139
Investments, amortized cost	2,139
Investments at fair value	$ 2,139
Investment, Issuer Name [Extensible Enumeration]	bcsf:AllworthFinancialGroupLPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan Delayed Draw [Member]		First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]	First Lien Senior Secured Loan Delayed Draw [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Amspec Services, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%		9.42%	9.42%	9.42%	9.42%
Maturity date	Jul. 02, 2024		Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024	Jul. 02, 2024
Principal/Shares	$ 9,796
Investments, amortized cost	9,796
Investments at fair value	$ 9,796
Investment, Issuer Name [Extensible Enumeration]	Amspec Services Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas [Member]		Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Apollo Intelligence First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.26%		8.26%	8.26%	8.26%	8.26%
Maturity date	Jun. 01, 2028		Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028	Jun. 01, 2028
Principal/Shares	$ 10,800
Investments, amortized cost	10,696
Investments at fair value	$ 10,692
Investment, Issuer Name [Extensible Enumeration]	Apollo Intelligence [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Aramsco, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.25%		5.25%	5.25%	5.25%	5.25%
Interest rate	8.37%		8.37%	8.37%	8.37%	8.37%
Maturity date	Aug. 28, 2024		Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024	Aug. 28, 2024
Principal/Shares	$ 9,509
Investments, amortized cost	9,509
Investments at fair value	$ 9,509
Investment, Issuer Name [Extensible Enumeration]	Aramsco Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Wholesale		Wholesale	Wholesale	Wholesale	Wholesale
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Avalon Acquiror, Inc. First Lien Senior Secured Loan
Investments
Interest rate	9.80%		9.80%	9.80%	9.80%	9.80%
Maturity date	Mar. 10, 2028		Mar. 10, 2028	Mar. 10, 2028	Mar. 10, 2028	Mar. 10, 2028
Principal/Shares	$ 22,743
Investments, amortized cost	22,529
Investments at fair value	$ 22,344
Investment, Issuer Name [Extensible Enumeration]	Avalon Acquiror, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Batteries Plus Holding Corporation First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.75%		6.75%	6.75%	6.75%	6.75%
Interest rate	9.87%		9.87%	9.87%	9.87%	9.87%
Maturity date	Jun. 30, 2023		Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Jun. 30, 2023
Principal/Shares	$ 10,500
Investments, amortized cost	10,500
Investments at fair value	$ 10,500
Investment, Issuer Name [Extensible Enumeration]	Batteries Plus Holding Corporation [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Blackbrush Oil & Gas, L.P. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	9.11%		9.11%	9.11%	9.11%	9.11%
Maturity date	Sep. 03, 2025		Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025
Principal/Shares	$ 4,394
Investments, amortized cost	4,394
Investments at fair value	$ 4,394
PIK	2.00%		2.00%	2.00%	2.00%	2.00%
Investment, Issuer Name [Extensible Enumeration]	bcsf:BlackbrushOilGasLPMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Energy Oil And Gas [Member]		Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]	Energy Oil And Gas [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: CPS Group Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%		9.42%	9.42%	9.42%	9.42%
Maturity date	Mar. 03, 2025		Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025	Mar. 03, 2025
Principal/Shares	$ 9,776
Investments, amortized cost	9,776
Investments at fair value	$ 9,776
Investment, Issuer Name [Extensible Enumeration]	C P S Group Holdings, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: CST Buyer Company First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	8.62%		8.62%	8.62%	8.62%	8.62%
Maturity date	Oct. 03, 2025		Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025	Oct. 03, 2025
Principal/Shares	$ 10,823
Investments, amortized cost	10,823
Investments at fair value	$ 10,823
Investment, Issuer Name [Extensible Enumeration]	C S T Buyer Company [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]		Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Cardo First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	7.09%		7.09%	7.09%	7.09%	7.09%
Maturity date	May 12, 2028		May 12, 2028	May 12, 2028	May 12, 2028	May 12, 2028
Principal/Shares	$ 10,800
Investments, amortized cost	10,800
Investments at fair value	$ 10,800
Investment, Issuer Name [Extensible Enumeration]	bcsf:CardoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]		Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Concert Golf Partners Holdco L L C First Lien Senior Secured Loan
Investments
Interest rate	6.50%		6.50%	6.50%	6.50%	6.50%
Maturity date	Mar. 30, 2029		Mar. 30, 2029	Mar. 30, 2029	Mar. 30, 2029	Mar. 30, 2029
Principal/Shares	$ 20,748
Investments, amortized cost	20,345
Investments at fair value	$ 20,541
Investment, Issuer Name [Extensible Enumeration]	bcsf:ConcertGolfPartnersHoldcoMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Conterra Ultra Broadband Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Interest rate	7.78%		7.78%	7.78%	7.78%	7.78%
Maturity date	Apr. 27, 2027		Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027
Principal/Shares	$ 6,272
Investments, amortized cost	6,076
Investments at fair value	$ 6,071
Investment, Issuer Name [Extensible Enumeration]	bcsf:ConterraUltraBroadbandHoldingsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Drilling Info Holdings, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.25%		4.25%	4.25%	4.25%	4.25%
Interest rate	7.37%		7.37%	7.37%	7.37%	7.37%
Maturity date	Jul. 30, 2025		Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025	Jul. 30, 2025
Principal/Shares	$ 10,802
Investments, amortized cost	10,713
Investments at fair value	$ 10,451
Investment, Issuer Name [Extensible Enumeration]	bcsf:DrillingInfoHoldingsIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Eagle Parent Corp First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.25%		4.25%	4.25%	4.25%	4.25%
Interest rate	7.80%		7.80%	7.80%	7.80%	7.80%
Maturity date	Mar. 19, 2029		Mar. 19, 2029	Mar. 19, 2029	Mar. 19, 2029	Mar. 19, 2029
Principal/Shares	$ 3,352
Investments, amortized cost	3,341
Investments at fair value	$ 3,269
Investment, Issuer Name [Extensible Enumeration]	bcsf:EagleParentCorpMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]		Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: FL Hawk Intermediate Holdings, Inc. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%		9.00%	9.00%	9.00%	9.00%
Interest rate	12.42%		12.42%	12.42%	12.42%	12.42%
Maturity date	Aug. 22, 2028		Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028	Aug. 22, 2028
Principal/Shares	$ 6,000
Investments, amortized cost	6,000
Investments at fair value	$ 6,000
Investment, Issuer Name [Extensible Enumeration]	bcsf:FLHawkIntermediateHoldingsIncMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Grammer Purchaser, Inc First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%		4.50%	4.50%	4.50%	4.50%
Interest rate	7.57%		7.57%	7.57%	7.57%	7.57%
Maturity date	Sep. 30, 2024		Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024
Principal/Shares	$ 3,475
Investments, amortized cost	3,475
Investments at fair value	$ 3,467
Investment, Issuer Name [Extensible Enumeration]	Grammer Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Grammer Purchaser, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Sep. 30, 2024		Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2024
Investments at fair value	$ (1)
Investment, Issuer Name [Extensible Enumeration]	Grammer Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Green Street Parent, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	8.62%		8.62%	8.62%	8.62%	8.62%
Maturity date	Aug. 27, 2026		Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026	Aug. 27, 2026
Principal/Shares	$ 10,670
Investments, amortized cost	10,670
Investments at fair value	$ 10,777
Investment, Issuer Name [Extensible Enumeration]	Green Street Parent, L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Banking [Member]		Banking [Member]	Banking [Member]	Banking [Member]	Banking [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Iris Holding, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Interest rate	7.89%		7.89%	7.89%	7.89%	7.89%
Maturity date	Jun. 15, 2028		Jun. 15, 2028	Jun. 15, 2028	Jun. 15, 2028	Jun. 15, 2028
Principal/Shares	$ 10,000
Investments, amortized cost	9,521
Investments at fair value	$ 9,220
Investment, Issuer Name [Extensible Enumeration]	bcsf:IrisHoldingInc.Member
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Containers Packaging And Glass [Member]		Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]	Containers Packaging And Glass [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: JHCC Holdings, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%		9.42%	9.42%	9.42%	9.42%
Maturity date	Sep. 09, 2025		Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025	Sep. 09, 2025
Principal/Shares	$ 7,540
Investments, amortized cost	7,540
Investments at fair value	$ 7,314
Investment, Issuer Name [Extensible Enumeration]	bcsf:JHCCHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Automotive Sector [Member]		Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]	Automotive Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: MZR Buyer, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.75%		6.75%	6.75%	6.75%	6.75%
Interest rate	10.42%		10.42%	10.42%	10.42%	10.42%
Maturity date	Dec. 21, 2026		Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026	Dec. 21, 2026
Principal/Shares	$ 23,075
Investments, amortized cost	23,075
Investments at fair value	$ 23,075
Investment, Issuer Name [Extensible Enumeration]	bcsf:MZRBuyerLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Consumer [Business]		Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]	Services, Consumer [Business]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: McLarensAcquisitionInc.FirstLienSeniorSecuredLoan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.03%		8.03%	8.03%	8.03%	8.03%
Maturity date	Dec. 19, 2024		Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024	Dec. 19, 2024
Principal/Shares	$ 10,479
Investments, amortized cost	10,479
Investments at fair value	$ 10,426
Investment, Issuer Name [Extensible Enumeration]	bcsf:McLarensAcquisitionIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Fire Finance		Fire Finance	Fire Finance	Fire Finance	Fire Finance
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Meriplex Communications Ltd First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	7.95%		7.95%	7.95%	7.95%	7.95%
Maturity date	Jul. 17, 2028		Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028	Jul. 17, 2028
Principal/Shares	$ 12,000
Investments, amortized cost	11,764
Investments at fair value	$ 11,760
Investment, Issuer Name [Extensible Enumeration]	Meriplex Communications Ltd. [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Telecommunications [Member]		Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]	Telecommunications [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Morrow Sodali Global L L C First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	7.69%		7.69%	7.69%	7.69%	7.69%
Maturity date	Apr. 25, 2028		Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028	Apr. 25, 2028
Principal/Shares	$ 7,959
Investments, amortized cost	7,844
Investments at fair value	$ 7,840
Investment, Issuer Name [Extensible Enumeration]	Morrow Sodali [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Banking Finance Insurance And Real Estate Sector [Member]		Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]	Banking Finance Insurance And Real Estate Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Omni Intermediate First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.00%		5.00%	5.00%	5.00%	5.00%
Interest rate	8.69%		8.69%	8.69%	8.69%	8.69%
Maturity date	Nov. 23, 2026		Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026	Nov. 23, 2026
Principal/Shares	$ 7,251
Investments, amortized cost	7,251
Investments at fair value	$ 7,251
Investment, Issuer Name [Extensible Enumeration]	bcsf:OmniIntermediateHoldingsLlcMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Omni Intermediate Holdings L L C Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%		9.00%	9.00%	9.00%	9.00%
Interest rate	12.69%		12.69%	12.69%	12.69%	12.69%
Maturity date	Dec. 30, 2027		Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027	Dec. 30, 2027
Principal/Shares	$ 5,000
Investments, amortized cost	5,000
Investments at fair value	$ 5,000
Investment, Issuer Name [Extensible Enumeration]	bcsf:OmniIntermediateHoldingsLlcMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Transportation Cargo [Member]		Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]	Transportation Cargo [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Quidditch Acquisition, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.00%		7.00%	7.00%	7.00%	7.00%
Interest rate	9.52%		9.52%	9.52%	9.52%	9.52%
Maturity date	Mar. 21, 2025		Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025	Mar. 21, 2025
Principal/Shares	$ 9,387
Investments, amortized cost	9,288
Investments at fair value	$ 9,340
Investment, Issuer Name [Extensible Enumeration]	bcsf:QuidditchAcquisitionIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Refine Intermediate, Inc. First Lien Senior Secured Loan
Investments
Interest rate	8.17%		8.17%	8.17%	8.17%	8.17%
Maturity date	Mar. 03, 2027		Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027	Mar. 03, 2027
Principal/Shares	$ 20,800
Investments, amortized cost	20,800
Investments at fair value	$ 20,800
Investment, Issuer Name [Extensible Enumeration]	Refine Intermediate, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: RoC Opco LLCFirst Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	8.50%		8.50%	8.50%	8.50%	8.50%
Interest rate	12.17%		12.17%	12.17%	12.17%	12.17%
Maturity date	Feb. 25, 2025		Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025	Feb. 25, 2025
Principal/Shares	$ 8,775
Investments, amortized cost	8,775
Investments at fair value	$ 8,753
Investment, Issuer Name [Extensible Enumeration]	bcsf:RoCOpcoLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Robinson Helicopter First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Interest rate	9.63%		9.63%	9.63%	9.63%	9.63%
Maturity date	Jun. 30, 2028		Jun. 30, 2028	Jun. 30, 2028	Jun. 30, 2028	Jun. 30, 2028
Principal/Shares	$ 11,850
Investments, amortized cost	11,588
Investments at fair value	$ 11,613
Investment, Issuer Name [Extensible Enumeration]	bcsf:RobinsonHelicopterMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Saltoun Franchise Holdings I L L C First Lien Senior Secured Loan
Investments
Interest rate	10.50%		10.50%	10.50%	10.50%	10.50%
Maturity date	Apr. 11, 2028		Apr. 11, 2028	Apr. 11, 2028	Apr. 11, 2028	Apr. 11, 2028
Principal/Shares	$ 10,455
Investments, amortized cost	10,417
Investments at fair value	$ 10,132
Investment, Issuer Name [Extensible Enumeration]	Saltoun [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Hotel, Gaming & Leisure		Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure	Hotel, Gaming & Leisure
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Saturn Purchaser Corp. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.60%		5.60%	5.60%	5.60%	5.60%
Interest rate	8.54%		8.54%	8.54%	8.54%	8.54%
Maturity date	Jul. 23, 2029		Jul. 23, 2029	Jul. 23, 2029	Jul. 23, 2029	Jul. 23, 2029
Principal/Shares	$ 12,000
Investments, amortized cost	11,882
Investments at fair value	$ 11,880
Investment, Issuer Name [Extensible Enumeration]	Saturn Purchaser Corp [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Smartronix L L C First Lien Senior Secured Loan
Investments
Interest rate	10.17%		10.17%	10.17%	10.17%	10.17%
Maturity date	Nov. 23, 2027		Nov. 23, 2027	Nov. 23, 2027	Nov. 23, 2027	Nov. 23, 2027
Principal/Shares	$ 13,101
Investments, amortized cost	12,862
Investments at fair value	$ 12,774
Investment, Issuer Name [Extensible Enumeration]	bcsf:SmartronixMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Solaray, LLC First Lien Senior Secured Loan
Investments
Interest rate	9.40%		9.40%	9.40%	9.40%	9.40%
Maturity date	Sep. 11, 2023		Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023	Sep. 11, 2023
Principal/Shares	$ 10,637
Investments, amortized cost	10,636
Investments at fair value	$ 10,583
Investment, Issuer Name [Extensible Enumeration]	Solaray L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Stanton Carpet Corp. Second Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	9.00%		9.00%	9.00%	9.00%	9.00%
Interest rate	12.75%		12.75%	12.75%	12.75%	12.75%
Maturity date	Apr. 01, 2028		Apr. 01, 2028	Apr. 01, 2028	Apr. 01, 2028	Apr. 01, 2028
Principal/Shares	$ 5,000
Investments, amortized cost	4,909
Investments at fair value	$ 5,000
Investment, Issuer Name [Extensible Enumeration]	bcsf:StantonCarpetMember
Investment, Type [Extensible Enumeration]	Second Lien Senior Secured Loan [Member]		Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]	Second Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]		Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: SunMed Group Holdings, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	9.42%		9.42%	9.42%	9.42%	9.42%
Maturity date	Jun. 16, 2028		Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028	Jun. 16, 2028
Principal/Shares	$ 9,655
Investments, amortized cost	9,655
Investments at fair value	$ 9,341
Investment, Issuer Name [Extensible Enumeration]	bcsf:SunMedGroupHoldingsLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Healthcare And Pharmaceuticals [Member]		Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]	Healthcare And Pharmaceuticals [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Superna Inc. First Lien Senior Secured Loan
Investments
Interest rate	9.52%		9.52%	9.52%	9.52%	9.52%
Maturity date	Mar. 06, 2028		Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028	Mar. 06, 2028
Principal/Shares	$ 21,691
Investments, amortized cost	21,491
Investments at fair value	$ 21,474
Investment, Issuer Name [Extensible Enumeration]	Superna Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: TEI Holdings Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.87%		8.87%	8.87%	8.87%	8.87%
Maturity date	Dec. 23, 2026		Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026	Dec. 23, 2026
Principal/Shares	$ 9,861
Investments, amortized cost	9,861
Investments at fair value	$ 9,861
Investment, Issuer Name [Extensible Enumeration]	T E I Holdings Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: TLC Purchaser, Inc.First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	11.54%		11.54%	11.54%	11.54%	11.54%
Maturity date	Oct. 13, 2025		Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025	Oct. 13, 2025
Principal/Shares	$ 9,871
Investments, amortized cost	8,910
Investments at fair value	$ 8,044
PIK	2.00%		2.00%	2.00%	2.00%	2.00%
Investment, Issuer Name [Extensible Enumeration]	T L C Purchaser, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Durable Sector [Member]		Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]	Consumer Goods Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Thrasio, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	7.00%		7.00%	7.00%	7.00%	7.00%
Interest rate	11.17%		11.17%	11.17%	11.17%	11.17%
Maturity date	Dec. 18, 2026		Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026	Dec. 18, 2026
Principal/Shares	$ 13,079
Investments, amortized cost	13,079
Investments at fair value	$ 12,033
Investment, Issuer Name [Extensible Enumeration]	bcsf:ThrasioLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Retail Sector		Retail Sector	Retail Sector	Retail Sector	Retail Sector
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: V Global Holdings LLCFirst Lien Senior Secured Loan
Investments
Interest rate	8.99%		8.99%	8.99%	8.99%	8.99%
Maturity date	Dec. 22, 2027		Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027	Dec. 22, 2027
Principal/Shares	$ 20,370
Investments, amortized cost	20,246
Investments at fair value	$ 20,014
Investment, Issuer Name [Extensible Enumeration]	V Global Holdings L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Chemicals, Plastics & Rubber		Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber	Chemicals, Plastics & Rubber
Investment, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]		Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Ventiv Holdco, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%		9.17%	9.17%	9.17%	9.17%
Maturity date	Sep. 03, 2025		Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025	Sep. 03, 2025
Principal/Shares	$ 9,823
Investments, amortized cost	9,823
Investments at fair value	$ 9,626
Investment, Issuer Name [Extensible Enumeration]	Ventiv Holdco, Inc [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	High Tech Industries [Member]		High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]	High Tech Industries [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: WCI-Gigawatt Purchaser LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Interest rate	8.73%		8.73%	8.73%	8.73%	8.73%
Maturity date	Nov. 19, 2027		Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027	Nov. 19, 2027
Principal/Shares	$ 20,694
Investments, amortized cost	20,378
Investments at fair value	$ 20,228
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCIGigawattPurchaserMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Services, Business		Services, Business	Services, Business	Services, Business	Services, Business
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: WCI-HSG Purchaser, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%		4.50%	4.50%	4.50%	4.50%
Interest rate	7.62%		7.62%	7.62%	7.62%	7.62%
Maturity date	Feb. 24, 2025		Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025	Feb. 24, 2025
Principal/Shares	$ 8,644
Investments, amortized cost	8,644
Investments at fair value	$ 8,644
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCI-HSGPurchaserIncMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: WCI-HSG Purchaser, Inc. First Lien Senior Secured Loan - Revolver
Investments
Maturity date	Feb. 22, 2025		Feb. 22, 2025	Feb. 22, 2025	Feb. 22, 2025	Feb. 22, 2025
Investment, Issuer Name [Extensible Enumeration]	bcsf:WCI-HSGPurchaserIncMember
Investment, Type [Extensible Enumeration]	bcsf:FirstLienSeniorSecuredLoanRevolverMember		bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember	bcsf:FirstLienSeniorSecuredLoanRevolverMember
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: WSP Midco LLC First Lien Senior Secured Loan Libor
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Interest rate	9.37%		9.37%	9.37%	9.37%	9.37%
Maturity date	Apr. 27, 2027		Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027	Apr. 27, 2027
Principal/Shares	$ 6,157
Investments, amortized cost	6,061
Investments at fair value	$ 5,756
Investment, Issuer Name [Extensible Enumeration]	bcsf:WSPMidcoLLCMember
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Wholesale Sector [Member]		Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]	Consumer Goods Wholesale Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%		9.17%	9.17%	9.17%	9.17%
Maturity date	Mar. 26, 2026		Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026
Principal/Shares	$ 6,561
Investments, amortized cost	6,560
Investments at fair value	$ 6,232
Investment, Issuer Name [Extensible Enumeration]	WU Holdco, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: WU Holdco, Inc. First Lien Senior Secured Loan Libor One
Investments
Spread Above Index (as a percent)	5.50%		5.50%	5.50%	5.50%	5.50%
Interest rate	9.17%		9.17%	9.17%	9.17%	9.17%
Maturity date	Mar. 26, 2026		Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026	Mar. 26, 2026
Principal/Shares	$ 6,335
Investments, amortized cost	6,335
Investments at fair value	$ 6,019
Investment, Issuer Name [Extensible Enumeration]	WU Holdco, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Consumer Goods Non Durable Sector [Member]		Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]	Consumer Goods Non Durable Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: Whitcraft LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Interest rate	9.67%		9.67%	9.67%	9.67%	9.67%
Maturity date	Apr. 03, 2023		Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023	Apr. 03, 2023
Principal/Shares	$ 10,710
Investments, amortized cost	10,550
Investments at fair value	$ 10,228
Investment, Issuer Name [Extensible Enumeration]	Whitcraft L L C [Member]
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	Aerospace and Defense Sector [Member]		Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]	Aerospace and Defense Sector [Member]
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Investment, Identifier [Axis]: YLG Holdings, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.25%		5.25%	5.25%	5.25%	5.25%
Interest rate	7.10%		7.10%	7.10%	7.10%	7.10%
Maturity date	Oct. 31, 2025		Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025	Oct. 31, 2025
Principal/Shares	$ 10,561
Investments, amortized cost	10,561
Investments at fair value	$ 10,535
Investment, Issuer Name [Extensible Enumeration]	YLG Holdings, Inc.
Investment, Type [Extensible Enumeration]	First Lien Senior Secured Loan [Member]		First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]	First Lien Senior Secured Loan [Member]
Investment, Industry Sector [Extensible Enumeration]	bcsf:ConstructionAndBuildingSectorMember		bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember	bcsf:ConstructionAndBuildingSectorMember
Investment, Variable Interest Rate, Type [Extensible Enumeration]	London Interbank Offered Rate (LIBOR) [Member]		London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]	London Interbank Offered Rate (LIBOR) [Member]
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: A R Logistics Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Allworth Financial Group, L.P. First Lien Senior Secured Loan - Delayed Draw
Investments
Spread Above Index (as a percent)	4.75%		4.75%	4.75%	4.75%	4.75%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Avalon Acquiror, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.25%		6.25%	6.25%	6.25%	6.25%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Concert Golf Partners Holdco L L C First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Refine Intermediate, Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	4.50%		4.50%	4.50%	4.50%	4.50%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Saltoun Franchise Holdings I L L C First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	10.50%		10.50%	10.50%	10.50%	10.50%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Smartronix L L C First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.00%		6.00%	6.00%	6.00%	6.00%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Solaray, LLC First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: Superna Inc. First Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	6.50%		6.50%	6.50%	6.50%	6.50%
Bain Capital Senior Loan Program, LLC | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Investment, Identifier [Axis]: V Global Holdings LLCFirst Lien Senior Secured Loan
Investments
Spread Above Index (as a percent)	5.75%		5.75%	5.75%	5.75%	5.75%
Bain Capital Senior Loan Program, LLC | Aerospace Sector [Member]
Investments
Investments, amortized cost	$ 42,664
Investments at fair value	$ 42,365
% of Member's Equity	160.80%		160.80%	160.80%	160.80%	160.80%
Bain Capital Senior Loan Program, LLC | Automotive Sector [Member]
Investments
Investments, amortized cost	$ 29,163
Investments at fair value	$ 28,937
% of Member's Equity	109.80%		109.80%	109.80%	109.80%	109.80%
Bain Capital Senior Loan Program, LLC | Banking [Member]
Investments
Investments, amortized cost	$ 10,670
Investments at fair value	$ 10,777
% of Member's Equity	40.90%		40.90%	40.90%	40.90%	40.90%
Bain Capital Senior Loan Program, LLC | Banking Finance Insurance And Real Estate Sector [Member]
Investments
Investments, amortized cost	$ 7,844
Investments at fair value	$ 7,840
% of Member's Equity	29.80%		29.80%	29.80%	29.80%	29.80%
Bain Capital Senior Loan Program, LLC | Chemicals, Plastics & Rubber
Investments
Investments, amortized cost	$ 20,246
Investments at fair value	$ 20,014
% of Member's Equity	76.00%		76.00%	76.00%	76.00%	76.00%
Bain Capital Senior Loan Program, LLC | Construction and Building
Investments
Investments, amortized cost	$ 10,561
Investments at fair value	$ 10,535
% of Member's Equity	40.00%		40.00%	40.00%	40.00%	40.00%
Bain Capital Senior Loan Program, LLC | Consumer Sector, Durable
Investments
Investments, amortized cost	$ 13,819
Investments at fair value	$ 13,044
% of Member's Equity	49.50%		49.50%	49.50%	49.50%	49.50%
Bain Capital Senior Loan Program, LLC | Consumer Sector, Non-Durable
Investments
Investments, amortized cost	$ 38,306
Investments at fair value	$ 37,587
% of Member's Equity	142.60%		142.60%	142.60%	142.60%	142.60%
Bain Capital Senior Loan Program, LLC | Consumer Sector, Wholesale
Investments
Investments, amortized cost	$ 6,061
Investments at fair value	$ 5,756
% of Member's Equity	21.80%		21.80%	21.80%	21.80%	21.80%
Bain Capital Senior Loan Program, LLC | Containers, Packaging and Glass
Investments
Investments, amortized cost	$ 32,394
Investments at fair value	$ 32,156
% of Member's Equity	122.00%		122.00%	122.00%	122.00%	122.00%
Bain Capital Senior Loan Program, LLC | Energy: Oil and Gas
Investments
Investments, amortized cost	$ 14,190
Investments at fair value	$ 14,190
% of Member's Equity	53.80%		53.80%	53.80%	53.80%	53.80%
Bain Capital Senior Loan Program, LLC | Fire Finance
Investments
Investments, amortized cost	$ 10,591
Investments at fair value	$ 10,591
% of Member's Equity	40.20%		40.20%	40.20%	40.20%	40.20%
Bain Capital Senior Loan Program, LLC | Fire Insurance
Investments
Investments, amortized cost	$ 10,479
Investments at fair value	$ 10,426
% of Member's Equity	39.60%		39.60%	39.60%	39.60%	39.60%
Bain Capital Senior Loan Program, LLC | Healthcare and Pharmaceuticals
Investments
Investments, amortized cost	$ 30,127
Investments at fair value	$ 29,809
% of Member's Equity	113.10%		113.10%	113.10%	113.10%	113.10%
Bain Capital Senior Loan Program, LLC | High Tech Industries
Investments
Investments, amortized cost	$ 50,953
Investments at fair value	$ 50,477
% of Member's Equity	191.60%		191.60%	191.60%	191.60%	191.60%
Bain Capital Senior Loan Program, LLC | Hotel, Gaming & Leisure
Investments
Investments, amortized cost	$ 45,630
Investments at fair value	$ 45,683
% of Member's Equity	173.40%		173.40%	173.40%	173.40%	173.40%
Bain Capital Senior Loan Program, LLC | Retail Sector
Investments
Investments, amortized cost	$ 23,579
Investments at fair value	$ 22,533
% of Member's Equity	85.50%		85.50%	85.50%	85.50%	85.50%
Bain Capital Senior Loan Program, LLC | Services, Business
Investments
Investments, amortized cost	$ 86,430
Investments at fair value	$ 86,007
% of Member's Equity	326.30%		326.30%	326.30%	326.30%	326.30%
Bain Capital Senior Loan Program, LLC | Services, Consumer [Business]
Investments
Investments, amortized cost	$ 26,416
Investments at fair value	$ 26,344
% of Member's Equity	100.00%		100.00%	100.00%	100.00%	100.00%
Bain Capital Senior Loan Program, LLC | Transportation Sector
Investments
Investments, amortized cost	$ 26,422
Investments at fair value	$ 26,413
% of Member's Equity	100.20%		100.20%	100.20%	100.20%	100.20%
Bain Capital Senior Loan Program, LLC | Telecommunications Sector [Member]
Investments
Investments, amortized cost	$ 17,840
Investments at fair value	$ 17,831
% of Member's Equity	67.70%		67.70%	67.70%	67.70%	67.70%
Bain Capital Senior Loan Program, LLC | Wholesale
Investments
Investments, amortized cost	$ 21,273
Investments at fair value	$ 21,269
% of Member's Equity	80.70%		80.70%	80.70%	80.70%	80.70%