INCOME TAXES - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended													12 Months Ended
	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Income Tax Contingency [Line Items]
Dividends				$ 20,900
Dividends declared (in usd per share)				$ 0.58
Undistributed ordinary income - tax basis				$ 16,070				$ 12,682				$ 21,083					$ 16,070		$ 12,682		$ 21,083
Cumulative undistributed taxable income (in usd per share)				$ 0.45													$ 0.45
Cost of investments				$ 1,210,800				852,400									$ 1,210,800		852,400
Gross unrealized appreciation				72,300				67,800									72,300		67,800
Gross unrealized depreciation				(76,800)				(61,700)									(76,800)		(61,700)
Net unrealized appreciation (depreciation)				(4,500)				6,100									(4,500)		6,100
Deferred tax liability				12,117				$ 5,747									12,117		5,747
Income tax provision																	329		615		2,442
Excise tax																	630		65		637
Dividends cash paid (in usd per share)					$ 0.57	$ 0.50	$ 0.63	$ 0.48	$ 0.97	$ 0.54	$ 0.53	$ 0.52	$ 0.51	$ 0.51	$ 0.51	$ 0.51		$ 2.18		$ 2.56		$ 2.04
RIC
Income Tax Contingency [Line Items]
Cost of investments				1,172,700													1,172,700
Gross unrealized appreciation				10,500													10,500
Gross unrealized depreciation				(72,300)													(72,300)
Net unrealized appreciation (depreciation)				(61,800)													(61,800)
Taxable Subsidiary
Income Tax Contingency [Line Items]
Cost of investments				38,100													38,100
Gross unrealized appreciation				61,800													61,800
Gross unrealized depreciation				(4,500)													(4,500)
Net unrealized appreciation (depreciation)				$ 57,300													57,300
Income tax provision																	$ (300)		$ 500		$ 1,800
Regular dividends
Income Tax Contingency [Line Items]
Dividends declared (in usd per share)				$ 0.53
Dividends cash paid (in usd per share)	$ 0.52	$ 0.48	$ 0.47
Interest-related Dividends
Income Tax Contingency [Line Items]
Percent of ordinary distributions																		89.74%		87.40%
Non-U.S. residents and foreign corporation shareholders
Income Tax Contingency [Line Items]
Percent of ordinary distributions																		89.74%		87.40%
Supplemental dividends
Income Tax Contingency [Line Items]
Dividends declared (in usd per share)				$ 0.05
Dividends cash paid (in usd per share)	$ 0.05		$ 0.50							$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.10