BORROWINGS - Borrowings Outstanding (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Debt Instrument [Line Items]
Outstanding Balance	$ 969,875	$ 779,875
Unamortized Debt Issuance Costs and Debt Discount/Premium	(13,810)	(9,022)
Recorded Value	956,065	770,853
Estimated Fair Value	939,710	726,298
SBA Debentures
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(4,082)	(4,305)
SBA Debentures | Unsecured Debt
Debt Instrument [Line Items]
Outstanding Balance	175,000	153,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	(4,082)	(4,305)
Recorded Value	170,918	148,695
Estimated Fair Value	166,460	141,638
Corporate Credit Facility | Line of Credit | Corporate Credit Facility
Debt Instrument [Line Items]
Outstanding Balance	235,000	265,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	0	0
Recorded Value	235,000	265,000
Estimated Fair Value	235,000	265,000
Interest expense	13,655	16,661	$ 11,156
SPV Credit Facility | Line of Credit | SPV Credit Facility
Debt Instrument [Line Items]
Outstanding Balance	108,000	0
Unamortized Debt Issuance Costs and Debt Discount/Premium	0	0
Recorded Value	108,000	0
Estimated Fair Value	108,000	0
Interest expense	6,118	0	0
January 2026 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	0	(612)
January 2026 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance		140,000
Unamortized Debt Issuance Costs and Debt Discount/Premium		(612)
Recorded Value		139,388
Estimated Fair Value		118,249
Interest expense	4,358	6,300	6,300
October 2026 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(1,154)	(1,923)
October 2026 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance	150,000	150,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	(1,154)	(1,923)
Recorded Value	148,846	148,077
Estimated Fair Value	130,899	127,150
Interest expense	5,062	5,062	5,062
August 2028 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(1,681)	(2,182)
August 2028 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance	71,875	71,875
Unamortized Debt Issuance Costs and Debt Discount/Premium	(1,681)	(2,182)
Recorded Value	70,194	69,693
Estimated Fair Value	73,571	74,261
Interest expense	5,570	4,425	0
2029 Convertible Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium	(6,893)	0
2029 Convertible Notes | Convertible Debt
Debt Instrument [Line Items]
Outstanding Balance	230,000
Unamortized Debt Issuance Costs and Debt Discount/Premium	(6,893)
Recorded Value	223,107
Estimated Fair Value	225,780
Interest expense	$ 4,650	$ 0	$ 0