BORROWINGS - Borrowings Outstanding (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Aug. 31, 2021	Sep. 30, 2025	Mar. 31, 2025
Debt Instrument [Line Items]
Outstanding Balance		$ 1,053,875	$ 969,875
Unamortized Debt Issuance Costs and Debt Discount/Premium		(19,117)	(13,810)
Recorded Value		1,034,758	956,065
Estimated Fair Value		1,037,998	939,710
SBA Debentures
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium		(4,088)	(4,082)
SBA Debentures | Unsecured Debt
Debt Instrument [Line Items]
Outstanding Balance		175,000	175,000
Unamortized Debt Issuance Costs and Debt Discount/Premium		(4,088)	(4,082)
Recorded Value		170,912	170,918
Estimated Fair Value		168,628	166,460
Corporate Credit Facility | Line of Credit | Corporate Credit Facility
Debt Instrument [Line Items]
Outstanding Balance		0	235,000
Unamortized Debt Issuance Costs and Debt Discount/Premium		0	0
Recorded Value		0	235,000
Estimated Fair Value		0	235,000
SPV Credit Facility | Line of Credit | SPV Credit Facility
Debt Instrument [Line Items]
Outstanding Balance		77,000	108,000
Unamortized Debt Issuance Costs and Debt Discount/Premium		0	0
Recorded Value		77,000	108,000
Estimated Fair Value		77,000	108,000
October 2026 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium		(769)	(1,154)
October 2026 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance		150,000	150,000
Unamortized Debt Issuance Costs and Debt Discount/Premium		(769)	(1,154)
Recorded Value		149,231	148,846
Estimated Fair Value		$ 150,000	130,899
Redemption price, percentage	100.00%	100.00%
August 2028 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium		$ (1,429)	(1,681)
August 2028 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance		71,875	71,875
Unamortized Debt Issuance Costs and Debt Discount/Premium		(1,429)	(1,681)
Recorded Value		70,446	70,194
Estimated Fair Value		72,860	73,571
2029 Convertible Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium		(6,153)	(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		(6,153)	(6,893)
Recorded Value		223,847	223,107
Estimated Fair Value		$ 221,944	225,780
Redemption price, percentage		100.00%
September 2030 Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs and Debt Discount/Premium		$ (6,678)	$ 0
September 2030 Notes | Notes
Debt Instrument [Line Items]
Outstanding Balance		350,000
Unamortized Debt Issuance Costs and Debt Discount/Premium		(6,678)
Recorded Value		343,322
Estimated Fair Value		$ 347,566
Redemption price, percentage	100.00%