BORROWINGS - Narrative (Details)					1 Months Ended		3 Months Ended		6 Months Ended
	Mar. 20, 2024 USD ($)	Mar. 01, 2024	Aug. 02, 2023 USD ($)	Apr. 20, 2021 USD ($)	Aug. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2024 USD ($) facility	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) facility	Sep. 30, 2023 USD ($)	Sep. 12, 2024 USD ($) lender	Sep. 11, 2024 USD ($)	Jun. 20, 2024 USD ($)	Jun. 19, 2024 USD ($)	Dec. 20, 2023 USD ($)	Dec. 07, 2023 USD ($) lender	Dec. 06, 2023 USD ($)	Aug. 01, 2023 USD ($)	Jun. 30, 2023 USD ($)	Nov. 22, 2022 USD ($)	Jan. 28, 2022 USD ($)	Nov. 30, 2021 USD ($)	May 25, 2021 USD ($)	Feb. 28, 2021 USD ($)	Apr. 25, 2019
Debt Instrument [Line Items]
Asset coverage ratio																									166.00%
Current asset coverage ratio							224.00%		224.00%
January 2026 Notes | Notes
Debt Instrument [Line Items]
Weighted average effective interest rate							4.46%	4.46%	4.46%	4.46%
Aggregate principal amount						$ 75,000,000																		$ 65,000,000
Fixed interest rate						4.50%
Issuance price percent received																								102.11%
Yield-to-maturity																								4.00%
Redemption price, percentage						100.00%
October 2026 Notes | Notes
Debt Instrument [Line Items]
Weighted average effective interest rate							3.50%	3.50%	3.50%	3.50%
Aggregate principal amount					$ 100,000,000																	$ 50,000,000
Fixed interest rate					3.375%																	3.375%
Issuance price percent received					99.418%																	99.993%
Yield-to-maturity					3.50%																	3.375%
Redemption price, percentage					100.00%
August 2028 Notes | Notes
Debt Instrument [Line Items]
Weighted average effective interest rate							7.75%	7.75%	7.75%	7.75%
Aggregate principal amount																			$ 71,900,000
Fixed interest rate																			7.75%
August 2028 Notes Overallotment | Notes
Debt Instrument [Line Items]
Aggregate principal amount																			$ 9,400,000
SBA Debentures | Unsecured Debt
Debt Instrument [Line Items]
Weighted average effective interest rate							4.43%	4.23%	4.41%	4.09%
SBA Debentures | Unsecured Debt | SBIC I
Debt Instrument [Line Items]
Maturity				10 years
Regulatory maximum borrowing capacity				$ 175,000,000
Regulatory capital				$ 87,500,000			$ 87,500,000		$ 87,500,000
Leverage commitment amount							175,000,000		175,000,000						$ 45,000,000					$ 50,000,000	$ 40,000,000		$ 40,000,000
Available leverage commitment							87,500,000		87,500,000
Unused commitments							$ 22,000,000		$ 22,000,000
Corporate Credit Facility | Line of Credit
Debt Instrument [Line Items]
Weighted average effective interest rate							7.77%		7.78%
Average borrowings							$ 237,500,000		$ 237,200,000
Corporate Credit Facility | Corporate Credit Facility | Line of Credit
Debt Instrument [Line Items]
Number of revolving credit facility | facility							1		1
Weighted average effective interest rate							7.74%	7.70%	7.75%	7.52%
Average borrowings							$ 166,685,000	$ 185,054,000	$ 178,579,000	$ 106,120,000
Basis spread on variable rate			2.15%
Maximum borrowing capacity			$ 435,000,000								$ 485,000,000	$ 460,000,000				$ 460,000,000	$ 435,000,000	$ 400,000,000
Accordion feature increase limit			$ 750,000,000								$ 25,000,000					$ 25,000,000
Number of lenders | lender											11					10
Minimum senior coverage ratio		2.00
Maximum asset coverage ratio		1.50
Interest coverage ratio		2.00
Corporate Credit Facility | Corporate Credit Facility | Line of Credit | Minimum
Debt Instrument [Line Items]
Commitment fee percentage		0.50%
Corporate Credit Facility | Corporate Credit Facility | Line of Credit | Maximum
Debt Instrument [Line Items]
Commitment fee percentage		1.00%
Secured Debt | SPV Credit Facility | Line of Credit
Debt Instrument [Line Items]
Number of revolving credit facility | facility							1		1
Weighted average effective interest rate							7.85%	0.00%	7.87%	0.00%
Average borrowings							$ 70,826,000	$ 0	$ 58,617,000	$ 0
Maximum borrowing capacity	$ 150,000,000													$ 150,000,000
Accordion feature increase limit													$ 200,000,000
Accordion feature that allows increases (up to)	$ 400,000,000
Secured Debt | SPV Credit Facility | Line of Credit | Before March 20 2027
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%
Secured Debt | SPV Credit Facility | Line of Credit | After March 20 2027
Debt Instrument [Line Items]
Basis spread on variable rate	2.85%
Secured Debt | SPV Credit Facility | Line of Credit | Before April 20 2024
Debt Instrument [Line Items]
Commitment fee percentage	0.10%
Secured Debt | SPV Credit Facility | Line of Credit | After April 20 2024
Debt Instrument [Line Items]
Commitment fee percentage	0.35%