Financial Highlights - Schedule of Financial Highlights (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Feb. 20, 2024
Per Share Data:
Net Asset Value Per Share, Beginning Balance	$ 19.83	$ 21.12	$ 19.88	$ 19.5	$ 19.43
Net investment income after tax	2.3	1.93	1.67	1.8	1.83
Net realized and unrealized gains (losses) on investments, asset acquisition and forward contracts, net of taxes	0.03	(1.43)	1.27	0.18	(0.14)
Net increase (decrease) in net assets resulting from operations	2.33	0.5	2.94	1.98	1.69
Effects of First Eagle Alternative Capital BDC, Inc. acquisition (Note 13)	(0.3)
Distributions declared from net investment income	(1.81)	(1.79)	(1.69)	(1.64)	(1.64)
Effects of rounding	(0.01)		0.01	0.04	0.03
Offering Costs			(0.02)		(0.01)
Total increase (decrease) in net assets	0.21	(1.29)	1.24	0.38	0.07
Net Asset Value Per Share, Ending Balance	$ 20.04	$ 19.83	$ 21.12	$ 19.88	$ 19.5
Shares outstanding, end of period	37,061,547	30,887,360	30,887,360	20,862,314	13,358,289
Market value, end of period	$ 17.38	$ 12.78	$ 17.6	$ 14.57		$ 16.39
Weighted average shares outstanding (basic):	35,928,203	30,887,360	28,477,771	27,681,757	17,344,640
Weighted average shares outstanding (diluted):	35,928,203	30,887,360	28,477,771	27,681,757	17,344,640
Total return based on market value	52.37%	18.45%	32.46%	1.47%
Total return based on net asset value	10.19%	2.37%	14.74%	10.36%	8.81%
Ratio/Supplemental Data:
Net assets, end of period	$ 742,594	$ 612,541	$ 652,285	$ 560,000	$ 406,917
Ratio of total net expenses to average net assets	14.39%	8.96%	7.81%	5.34%	6.54%
Ratio of net expenses (without incentive fees and interest and other debt expenses) to average net assets	3.64%	3.26%	3.02%	2.24%	2.50%
Ratio of net investment income before taxes to average net assets	11.88%	9.41%	8.40%	10.10%	9.61%
Ratio of interest and credit facility expenses to average net assets	8.32%	5.01%	3.33%	3.10%	4.03%
Ratio of net incentive fees to average net assets	2.43%	0.68%	1.46%
Portfolio turnover	13.31%	21.52%	41.64%	28.01%	23.97%
Asset coverage ratio	186.00%	192.00%	201.00%	217.00%	225.00%