Financial Highlights - Schedule of Information about Senior Securities (Details) - USD ($)	Dec. 31, 2023	Jul. 28, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 27, 2021	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 29, 2015
Investment Company, Financial Highlights [Line Items]
Asset coverage per unit	$ 1,000,000
SPV Asset Facility
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities	329,850,000		$ 233,000,000	$ 249,500,000			$ 260,210,000	$ 220,687,000	$ 159,629,000	$ 86,629,000	$ 47,629,000
Asset coverage per unit	1,860,000		1,917,000	2,014,000			2,166,000	2,250,000	2,085,000	2,135,000	2,347,000
Revolving Credit Facility
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities											47,810,000	$ 54,810,000
Asset coverage per unit											$ 2,347,000	$ 2,415,000	$ 50,000,000
Revolving Credit Facility II
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities									78,310,000	65,310,000
Asset coverage per unit									$ 2,085,000	$ 2,135,000
Ally Corporate Revolving Facility
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities							149,904,000	104,754,000
Asset coverage per unit					$ 200,000,000		2,166,000	$ 2,250,000
SMBC Corporate Revolving Facility
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities	225,471,000		241,836,000	203,437,000
Asset coverage per unit	1,860,000		1,917,000	2,014,000
Series 2020A Notes
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities			50,000,000	50,000,000			50,000,000
Asset coverage per unit		$ 50,000,000	1,917,000	2,014,000			2,166,000
Series 2021A Notes
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities	135,000,000		135,000,000	135,000,000
Asset coverage per unit	1,860,000		$ 1,917,000	$ 2,014,000
Series 2023A Notes
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities	50,000,000
Asset coverage per unit	1,860,000
FCRX Unsecured Notes
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities	111,600,000
Asset coverage per unit	1,860,000
Average market value per unit	$ 941,000
InterNotes
Investment Company, Financial Highlights [Line Items]
Total amount outstanding exclusive of treasury securities							16,418,000
Asset coverage per unit						$ 16,400,000	$ 2,166,000