Consolidated Statements of Changes in Net Assets - USD ($) $ in Thousands	3 Months Ended										12 Months Ended						126 Months Ended
	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, 2022		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2022		Sep. 21, 2021	Sep. 20, 2021	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Changes in net assets from operations:
Net investment income	$ 23,877		$ 25,557	$ 19,288	$ 19,483	$ 18,410		$ 19,612	$ 18,686	$ 17,599	$ 88,205		$ 74,307		$ 78,728
Net realized (loss) gain on investments											(32,747)		843		(69,898)
Net realized (loss) gain on foreign currency											(3)		(3)		26
Net change in unrealized (depreciation) appreciation on investments											(5,314)		43,617		(19,878)
Net increase (decrease) in net assets resulting from operations											50,141		118,764		(11,022)
Changes in net assets from shareholders' distributions:
Net decrease in net assets resulting from shareholders' distributions											(81,575)		(71,530)		(63,283)
Changes in net assets from capital share transactions:
Reinvestment of shareholders' distributions											0		15,489		23,298
Repurchase of common stock											(15,444)		(10,467)		(23,300)		$ (247,874)
Net (decrease) increase in net assets resulting from capital share transactions											(15,444)		5,022		(2)
Total (decrease) increase in net assets											(46,878)		52,256		(74,307)
Net assets at beginning of year					$ 930,512					$ 878,256	930,512		878,256		952,563
Net assets at end of year	$ 883,634					$ 930,512					$ 883,634		$ 930,512		$ 878,256		$ 883,634
Net asset value per share of common stock at end of year	$ 15.98	[1]				$ 16.34	[1]				$ 15.98	[1]	$ 16.34	[1]	$ 15.50	[1]	$ 15.98	[1]			$ 16.80	[1]	$ 17.38	$ 18.28
Shares of common stock outstanding at end of year (in shares)	55,299,484	[1]				56,958,440	[1]				55,299,484	[1]	56,958,440	[1]	56,646,867	[1]	55,299,484	[1]	56,958,440	113,916,869	56,690,578		56,354,579

[1] As discussed in Note 3, the Company completed a two-to-one reverse stock split, effective as of September 21, 2021. The shares outstanding used in the computation of net asset value per share reflect the reverse stock split on a retroactive basis.