INCOME TAXES - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Tax Contingency [Line Items]
Dividends	$ 24,800	$ 22,900	$ 20,900
Dividends declared (in usd per share)	$ 0.62	$ 0.59	$ 0.58
Cost of investments	$ 1,349,600		$ 1,210,800		$ 1,349,600
Gross unrealized appreciation	79,300		72,300		79,300
Gross unrealized depreciation	(75,300)		(76,800)		(75,300)
Net unrealized appreciation (depreciation)	4,000		(4,500)		4,000
Deferred tax liability	10,358		$ 12,117		10,358
Income tax provision (benefit)	(783)			$ 534	(336)	$ 726
Excise tax	100			200	300	300
RIC
Income Tax Contingency [Line Items]
Cost of investments	1,304,500				1,304,500
Gross unrealized appreciation	17,300				17,300
Gross unrealized depreciation	(71,000)				(71,000)
Net unrealized appreciation (depreciation)	(53,700)				(53,700)
Taxable Subsidiary
Income Tax Contingency [Line Items]
Cost of investments	45,100				45,100
Gross unrealized appreciation	62,000				62,000
Gross unrealized depreciation	(4,300)				(4,300)
Net unrealized appreciation (depreciation)	57,700				57,700
Income tax provision (benefit)	$ (900)			$ 300	$ (600)	$ 400
Regular Dividends
Income Tax Contingency [Line Items]
Dividends declared (in usd per share)	$ 0.56	0.54	$ 0.53
Supplemental Dividends
Income Tax Contingency [Line Items]
Dividends declared (in usd per share)	$ 0.06	$ 0.05	$ 0.05