BORROWINGS - Borrowings Outstanding (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Mar. 31, 2025
Debt Instrument [Line Items]
Outstanding Balance	$ 938,875	$ 969,875
Unamortized Debt Issuance Costs and Debt Discount/Premium	(12,925)	(13,810)
Recorded Value	925,950	956,065
Estimated Fair Value	905,262	939,710
SBA Debentures
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(3,885)	(4,082)
SBA Debentures | Unsecured Debt
Debt Instrument [Line Items]
Outstanding Balance	175,000	175,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	(3,885)	(4,082)
Recorded Value	171,115	170,918
Estimated Fair Value	166,547	166,460
Corporate Credit Facility | Line of Credit | Corporate Credit Facility
Debt Instrument [Line Items]
Outstanding Balance	200,000	235,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	0	0
Recorded Value	200,000	235,000
Estimated Fair Value	200,000	235,000
SPV Credit Facility | Line of Credit | SPV Credit Facility
Debt Instrument [Line Items]
Outstanding Balance	112,000	108,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	0	0
Recorded Value	112,000	108,000
Estimated Fair Value	112,000	108,000
October 2026 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(962)	(1,154)
October 2026 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance	150,000	150,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	(962)	(1,154)
Recorded Value	149,038	148,846
Estimated Fair Value	130,673	130,899
August 2028 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(1,555)	(1,681)
August 2028 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance	71,875	71,875
Unamortized Debt Issuance Costs and Debt Discount/Premium	(1,555)	(1,681)
Recorded Value	70,320	70,194
Estimated Fair Value	73,491	73,571
2029 Convertible Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(6,523)	(6,893)
2029 Convertible Notes | Convertible Debt
Debt Instrument [Line Items]
Outstanding Balance	230,000	230,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	(6,523)	(6,893)
Recorded Value	223,477	223,107
Estimated Fair Value	$ 222,551	$ 225,780