Investments - Schedule of Composition of Investment Portfolio (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Investment cost	$ 2,538,142	$ 2,607,174
Fair Value	2,334,199	2,398,120
Total Investments after Cash Equivalents	2,538,394
Total Investments after Cash Equivalents, Fair Value	2,334,451
Money Market Funds [Member]
Schedule of Investments [Line Items]
Total Cash Equivalents	252
Total Cash Equivalents, Fair Value	252
Level 1
Schedule of Investments [Line Items]
Fair Value	1,217	1,761
Total Investments after Cash Equivalents, Fair Value	1,469
Level 1 | Money Market Funds [Member]
Schedule of Investments [Line Items]
Total Cash Equivalents, Fair Value	252
Level 2
Schedule of Investments [Line Items]
Fair Value		323
Level 3
Schedule of Investments [Line Items]
Fair Value	2,332,982	2,396,036
Total Investments after Cash Equivalents, Fair Value	2,332,982
First Lien Secured Debt
Schedule of Investments [Line Items]
Investment cost	2,093,887	2,150,973
Fair Value	2,075,031	2,130,309
First Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	2,075,031	2,130,309
Second Lien Secured Debt
Schedule of Investments [Line Items]
Investment cost	46,274	105,731
Fair Value	31,887	70,919
Second Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	31,887	70,919
Unsecured Debt
Schedule of Investments [Line Items]
Investment cost		50
Fair Value		50
Unsecured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value		50
Structured Products And Other
Schedule of Investments [Line Items]
Investment cost	44,993	16,998
Fair Value	41,333	9,413
Structured Products And Other | Level 3
Schedule of Investments [Line Items]
Fair Value	41,333	9,413
Preferred Equity
Schedule of Investments [Line Items]
Investment cost	25,685	40,530
Fair Value	32,405	35,557
Preferred Equity | Level 3
Schedule of Investments [Line Items]
Fair Value	32,405	35,557
Common Equity/Interests
Schedule of Investments [Line Items]
Investment cost	326,914	292,503
Fair Value	153,344	151,398
Common Equity/Interests | Level 1
Schedule of Investments [Line Items]
Fair Value	1,217	1,761
Common Equity/Interests | Level 2
Schedule of Investments [Line Items]
Fair Value		323
Common Equity/Interests | Level 3
Schedule of Investments [Line Items]
Fair Value	152,127	149,314
Warrants - Warrants
Schedule of Investments [Line Items]
Investment cost	389	389
Fair Value	199	474
Warrants - Warrants | Level 3
Schedule of Investments [Line Items]
Fair Value	$ 199	$ 474