Debt and Foreign Currency Transactions and Translations - Schedule of Outstanding Debt Obligations (Details) - USD ($)					6 Months Ended		12 Months Ended
		Dec. 13, 2023	Jul. 16, 2021	Mar. 03, 2015	Jun. 30, 2024		Dec. 31, 2023
Debt Instrument [Line Items]
Total Aggregate Principal Amount Committed					$ 2,492,000,000		$ 2,492,000,000
Principal Amount Outstanding					1,518,176,000		1,469,977,000
Deferred Financing Costs and Debt Discount					(6,624,000)		(7,710,000)
Total Bethesda CLO 1 Notes					1,511,552,000		1,462,267,000
Fair Value of Debt Obligations					$ 1,509,059,000		$ 1,446,881,000
Senior Secured Facility
Debt Instrument [Line Items]
Date Issued/ Amended					Apr. 19, 2023		Apr. 19, 2023
Total Aggregate Principal Amount Committed					$ 1,705,000,000	[1]	$ 1,705,000,000	[2]
Principal Amount Outstanding					731,176,000	[3]	682,977,000	[4]
Fair Value of Debt Obligations					$ 731,176,000	[5]	$ 682,977,000	[6]
Final Maturity Date					Apr. 19, 2028		Apr. 19, 2028
Bethesda CLO 1 Class A-1
Debt Instrument [Line Items]
Date Issued/ Amended							Nov. 02, 2023
Total Aggregate Principal Amount Committed							$ 232,000,000
Principal Amount Outstanding							232,000,000
Fair Value of Debt Obligations	[7]						$ 232,000,000
Final Maturity Date							Oct. 23, 2035
MFIC Bethesda CLO I LLC Class A-1 Notes
Debt Instrument [Line Items]
Date Issued/ Amended					Nov. 02, 2023
Total Aggregate Principal Amount Committed					$ 232,000,000
Principal Amount Outstanding					232,000,000
Fair Value of Debt Obligations	[8]				$ 232,909,000
Final Maturity Date					Oct. 23, 2035
2025 Notes
Debt Instrument [Line Items]
Date Issued/ Amended					Mar. 03, 2015		Mar. 03, 2015
Total Aggregate Principal Amount Committed				$ 350,000,000	$ 350,000,000		$ 350,000,000
Principal Amount Outstanding					350,000,000		350,000,000
Fair Value of Debt Obligations					$ 346,555,000	[8]	$ 336,013,000	[7]
Final Maturity Date				Mar. 03, 2025	Mar. 03, 2025		Mar. 03, 2025
2026 Notes
Debt Instrument [Line Items]
Date Issued/ Amended					Jul. 16, 2021		Jul. 16, 2021
Total Aggregate Principal Amount Committed			$ 125,000,000		$ 125,000,000		$ 125,000,000
Principal Amount Outstanding					125,000,000		125,000,000
Fair Value of Debt Obligations					$ 117,907,000	[8]	$ 114,291,000	[7]
Final Maturity Date			Jul. 16, 2026		Jul. 16, 2026		Jul. 16, 2026
2028 Notes
Debt Instrument [Line Items]
Date Issued/ Amended					Dec. 13, 2023		Dec. 13, 2023
Total Aggregate Principal Amount Committed		$ 80,000,000			$ 80,000,000		$ 80,000,000
Principal Amount Outstanding					80,000,000		80,000,000
Fair Value of Debt Obligations					$ 80,512,000	[9]	$ 81,600,000	[10]
Final Maturity Date		Dec. 15, 2028			Dec. 15, 2028		Dec. 15, 2028

[1] Prior to November 19, 2022, total lender commitments were $1,810,000. As of June 30, 2024, total lender commitments were $1,705,000. The total lender commitments will remain $1,705,000 until December 22, 2024 and will decrease to $1,550,000 thereafter.

[2] Prior to November 19, 2022, total lender commitments were $1,810,000. As of December 31, 2023, total lender commitments were $1,705,000.

[3] Includes foreign currency debt obligations as outlined in Foreign Currency Transactions and Translations within this note to the consolidated financial statements.

[4] Includes foreign currency debt obligations as outlined in Foreign Currency Transactions and Translations within this note to the consolidated financial statements.

[5] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of June 30, 2024. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.

[6] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of December 31, 2023. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.

[7] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of December 31, 2023. The valuation is based on broker quoted prices.

[8] The fair value of these debt obligations would be categorized as Level 2 under ASC 820 as of June 30, 2024. The valuation is based on broker quoted prices.

[9] The fair value of these debt obligations would be categorized as Level 1 under ASC 820 as of June 30, 2024. The valuation is arrived using the closing price on exchange as on the relevant date.

[10] The fair value of these debt obligations would be categorized as Level 1 under ASC 820 as of December 31, 2023. The valuation is arrived using the closing price on exchange as on the relevant date.