INCOME TAXES - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Tax Contingency [Line Items]
Dividends	$ 14,300	$ 16,600	$ 11,800
Dividends (in usd per share)	$ 0.50
Cost of investments	$ 1,060,800		852,400		$ 1,060,800
Gross unrealized appreciation	58,900		67,800		58,900
Gross unrealized depreciation	(62,800)		(61,700)		(62,800)
Net unrealized appreciation (depreciation)	(3,900)		6,100		(3,900)
Deferred tax liability	8,798		$ 5,747		8,798
Income tax provision	534			$ 314	726	$ 710
Accrual for U.S. federal excise tax	200				300
Common Stock, Dividends, Per Share, Cash Paid		$ 0.63	$ 0.48
RIC
Income Tax Contingency [Line Items]
Cost of investments	1,033,800				1,033,800
Gross unrealized appreciation	16,700				16,700
Gross unrealized depreciation	(60,600)				(60,600)
Net unrealized appreciation (depreciation)	(43,900)				(43,900)
Taxable Subsidiary
Income Tax Contingency [Line Items]
Cost of investments	27,000				27,000
Gross unrealized appreciation	42,200				42,200
Gross unrealized depreciation	(2,200)				(2,200)
Net unrealized appreciation (depreciation)	40,000				40,000
Income tax provision	$ 300			$ 300	$ 400	$ 700
Regular Dividends
Income Tax Contingency [Line Items]
Common Stock, Dividends, Per Share, Cash Paid		0.48
Special Dividend
Income Tax Contingency [Line Items]
Common Stock, Dividends, Per Share, Cash Paid		$ 0.15