SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Quarterly Financial Information Disclosure [Abstract]
Net investment income	$ 27,842	$ 30,316	$ 31,165	$ 28,859	$ 29,396	$ 28,859	$ 27,194	$ 24,556	$ 118,182	$ 110,005	$ 68,711
Net realized (loss) gain on investments, net of tax	(27,267)	(12,805)	(10,289)	711	(19,661)	(7,842)	390	(12,782)	(49,650)	(39,895)	(17,029)
Net change in unrealized appreciation (depreciation) on investments, net of tax	16,997	(847)	1,808	(15,535)	3,734	2,467	(4,599)	12,038	2,423	13,640	(18,589)
Realized loss on extinguishment of debt	0	(387)	0	0	0	0	(361)	0	(387)	(361)	0
Realized loss on disposal of fixed assets	(11)	(9)	0	0					(20)	0	0
Net increase in net assets from operations	$ 17,561	$ 16,268	$ 22,684	$ 14,035	$ 13,469	$ 23,484	$ 22,624	$ 23,812	$ 70,548	$ 83,389	$ 33,093
Pre-tax net investment income per share - basic (in usd per share)	$ 0.56	$ 0.64	$ 0.64	$ 0.69	$ 0.68	$ 0.72	$ 0.67	$ 0.67	$ 2.50	$ 2.72	$ 2.30
Net investment income per share – basic (in usd per share)	0.54	0.63	0.66	0.63	0.67	0.70	0.69	0.65	2.46	2.70	2.29
Net increase in net assets from operations – basic (in usd per share)	0.34	0.34	0.48	0.31	0.31	0.57	0.57	0.63	1.47	2.05	1.10
Net increase in net assets from operations – diluted (in usd per share)	$ 0.35	$ 0.34	$ 0.48	$ 0.31	$ 0.31	$ 0.57	$ 0.57	$ 0.63	$ 1.47	$ 2.05	$ 1.10