Fair Value of Financial Instruments - Summarized Financial Information For SLF (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023		Mar. 31, 2022	Dec. 31, 2022		Dec. 31, 2021
ASSETS
Investments, at fair value (amortized cost of $929,893 and $923,304, respectively)	$ 2,900,567	[1]		$ 2,875,144	[2]
Investments at Amortized Cost	2,955,845	[1]		2,927,131	[2]
Total assets	3,001,974			2,979,878
LIABILITIES
Deferred financing costs	8,803			9,665
Total liabilities	1,320,535			1,314,421
MEMBERS' CAPITAL
Total members' capital	1,681,439		$ 1,498,382	1,665,457		$ 1,509,492
Total liabilities and net assets	3,001,974			2,979,878
Investment income
Total investment income	83,290		63,776
Operating expenses
Interest and debt fees	20,120		12,284
Total expenses	44,208		32,771
Net investment income	38,343		29,026
Realized and unrealized gain (loss)
Net realized and unrealized gain (loss)	(5,356)		5,901
FBLC Senior Loan Fund, LLC
ASSETS
Investments, at fair value (amortized cost of $929,893 and $923,304, respectively)	867,931			855,705
Investments at Amortized Cost	929,893			923,304
Cash and other assets	104,243			109,966
Total assets	972,174			965,671
LIABILITIES
Revolving credit facilities (net of deferred financing costs of $1,235 and $1,483, respectively)	537,815			549,067
Deferred financing costs	1,235			1,483
Secured borrowings	62,744			60,899
Other liabilities	27,904			20,264
Total liabilities	628,463			630,230
MEMBERS' CAPITAL
Total members' capital	343,711			335,441
Total liabilities and net assets	972,174			$ 965,671
Investment income
Total investment income	22,572		14,429
Operating expenses
Interest and debt fees	9,755		3,368
Other expenses	576		634
Total expenses	10,331		4,002
Net investment income	12,241		10,427
Realized and unrealized gain (loss)
Net realized and unrealized gain (loss)	4,539		(13,249)
Net increase (decrease) in members' capital resulting from operations	16,780		$ (2,822)
FBLC Senior Loan Fund, LLC
ASSETS
Investments, at fair value (amortized cost of $929,893 and $923,304, respectively)	304,934
Investments at Amortized Cost	$ 304,934

[1] Percentages are based on net assets as of March 31, 2023.

[2] Percentages are based on net assets as of December 31, 2022.