Financial Highlights - Schedule of Financial Highlights (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Per Share Data:
Par Amount	$ 19.83	$ 21.12
Net investment income after tax	0.54	0.39
Net realized and unrealized gains (losses) on investments, asset acquisition and forward contracts, net of taxes	(0.30)	0.13
Net increase (decrease) in net assets resulting from operations	0.24	0.52
Effects of First Eagle Alternative Capital BDC, Inc. acquisition (Note 13)	(0.28)
Distributions declared from net investment income	(0.41)	(0.46)
Total increase (decrease) in net assets	(0.45)	0.06
Par Amount	$ 19.38	$ 21.18
Shares outstanding, end of period	37,061,547	30,887,360
Market value, end of period	$ 13.62	$ 17.80
Weighted average shares outstanding (basic):	32,465,208	30,887,360
Weighted average shares outstanding (diluted):	32,465,208	30,887,360
Total return based on market value	(9.78%)	3.76%
Total return based on net asset value	0.20%	2.46%
Ratio/Supplemental Data:
Net assets, end of period	$ 718,420	$ 654,286
Ratio of total net expenses to average net assets	13.28%	8.84%
Ratio of net expenses (without incentive fees and interest and other debt expenses) to average net assets	3.54%	3.34%
Ratio of net investment income before taxes to average net assets	10.78%	7.63%
Ratio of interest and credit facility expenses to average net assets	7.54%	3.40%
Ratio of net incentive fees to average net assets	2.20%	2.11%
Portfolio turnover	2.16%	3.90%
Asset coverage ratio	181.00%	202.00%