Consolidated Statements of Changes in Net Assets - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Statement Of Partners Capital [Abstract]
Net assets at beginning of period	$ 1,585,672	$ 1,631,525	$ 1,614,400	$ 1,615,141
Increase (decrease) in net assets from operations:
Net investment income	61,189	64,332	160,951	180,091
Net realized gain (loss)	(1,475)	34,330	(9,331)	40,437
Net change in unrealized appreciation (depreciation)	(67,344)	(60,546)	(100,297)	(66,749)
(Provision) benefit for taxes on realized gain/loss on investments				(53)
(Provision) benefit for taxes on unrealized appreciation/depreciation on investments	130	(83)	12	(253)
Net increase (decrease) in net assets from operations	(7,500)	38,033	51,335	153,473
Distributions to stockholders from:
Distributable earnings	(46,250)	(50,876)	(138,033)	(152,513)
Total distributions to stockholders	(46,250)	(50,876)	(138,033)	(152,513)
Capital transactions:
Issuance of common stock (net of offering and underwriting costs)	10,560		12,352
Reinvestment of stockholder distributions	1,421	1,407	3,849	3,988
Net increase in net assets from capital transactions	11,981	1,407	16,201	3,988
Total increase (decrease) in net assets	(41,769)	(11,436)	(70,497)	4,948
Net assets at end of period	$ 1,543,903	$ 1,620,089	$ 1,543,903	$ 1,620,089
Distributions per share	$ 0.45	$ 0.50	$ 1.35	$ 1.50