Income Taxes - Increase in Net Assets From Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Increase (decrease) in net assets resulting from operations	$ 793,312	$ 466,355	$ 624,882
Net unrealized (gain) loss on investments	(92,900)	94,500	(179,800)
Other income (loss) for tax purposes, not book	(43,300)	(33,000)	(2,000)
Deferred organization costs	(100)	(100)	(100)
Other book-tax differences	12,700	5,800	4,000
Realized gain/loss differences	53,000	1,000	37,400
Taxable Income	$ 722,700	$ 534,500	$ 484,400