SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Quarterly Financial Information Disclosure [Abstract]
Net investment income	$ 29,396	$ 28,859	$ 27,194	$ 24,556	$ 22,404	$ 19,425	$ 14,444	$ 12,438	$ 110,005	$ 68,711	$ 42,687
Net realized (loss) gain on investments, net of tax	(19,661)	(7,842)	390	(12,782)	372	(11,086)	(8,635)	2,320	(39,895)	(17,029)	5,834
Net change in unrealized appreciation (depreciation) on investments, net of tax	3,734	2,467	(4,599)	12,038	(4,600)	(5,390)	3,649	(12,248)	13,640	(18,589)	11,467
Realized loss on extinguishment of debt	0	0	(361)	0					(361)	0	(17,087)
Net increase in net assets from operations	$ 13,469	$ 23,484	$ 22,624	$ 23,812	$ 18,176	$ 2,949	$ 9,458	$ 2,510	$ 83,389	$ 33,093	$ 42,815
Pre-tax net investment income per share - basic (in usd per share)	$ 0.68	$ 0.72	$ 0.67	$ 0.67	$ 0.65	$ 0.60	$ 0.54	$ 0.50	$ 2.72	$ 2.30	$ 1.90
Pre-tax net investment income per share - diluted (in usd per share)	0.68	0.72	0.67	0.67	0.65	0.60	0.54	0.50	2.72	2.30	1.90
Net investment income per share – basic (in usd per share)	0.67	0.70	0.69	0.65	0.64	0.62	0.52	0.49	2.70	2.29	1.87
Net investment income per share – diluted (in usd per share)	0.67	0.70	0.69	0.65	0.64	0.62	0.52	0.49	2.70	2.29	1.87
Net increase in net assets from operations – basic (in usd per share)	0.31	0.57	0.57	0.63	0.52	0.09	0.34	0.10	2.05	1.10	1.87
Net increase in net assets from operations – diluted (in usd per share)	$ 0.31	$ 0.57	$ 0.57	$ 0.63	$ 0.52	$ 0.09	$ 0.34	$ 0.10	$ 2.05	$ 1.10	$ 1.87