Investments - Schedule of Composition of Investment Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Investment cost	$ 2,552,527	$ 2,538,142
Fair Value	2,352,835	2,334,199
Total Cash Equivalents	255
Total Cash Equivalents, Fair Value	255
Total Investments after Cash Equivalents	2,552,782	2,538,394
Total Investments after Cash Equivalents, Fair Value	2,353,090	2,334,451
Money Market Funds [Member]
Schedule of Investments [Line Items]
Total Cash Equivalents	255	252
Total Cash Equivalents, Fair Value	255	252
Level 1
Schedule of Investments [Line Items]
Fair Value	1,514	1,217
Total Cash Equivalents, Fair Value	255
Total Investments after Cash Equivalents, Fair Value	1,769	1,469
Level 1 | Money Market Funds [Member]
Schedule of Investments [Line Items]
Total Cash Equivalents, Fair Value	255	252
Level 2
Schedule of Investments [Line Items]
Fair Value	7,900
Total Investments after Cash Equivalents, Fair Value	7,900
Level 3
Schedule of Investments [Line Items]
Fair Value	2,343,421	2,332,982
Total Investments after Cash Equivalents, Fair Value	2,343,421	2,332,982
First Lien Secured Debt
Schedule of Investments [Line Items]
Investment cost	2,125,753	2,093,887
Fair Value	2,111,478	2,075,031
First Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	2,111,478	2,075,031
Second Lien Secured Debt
Schedule of Investments [Line Items]
Investment cost	15,366	46,274
Fair Value	13,459	31,887
Second Lien Secured Debt | Level 2
Schedule of Investments [Line Items]
Fair Value	7,900
Second Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	5,559	31,887
Unsecured Debt
Schedule of Investments [Line Items]
Investment cost	2,664
Fair Value	329
Unsecured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	329
Structured Products And Other
Schedule of Investments [Line Items]
Investment cost	42,647	44,993
Fair Value	35,639	41,333
Structured Products And Other | Level 3
Schedule of Investments [Line Items]
Fair Value	35,639	41,333
Preferred Equity
Schedule of Investments [Line Items]
Investment cost	25,802	25,685
Fair Value	32,752	32,405
Preferred Equity | Level 3
Schedule of Investments [Line Items]
Fair Value	32,752	32,405
Common Equity/Interests
Schedule of Investments [Line Items]
Investment cost	339,330	326,914
Fair Value	158,920	153,344
Common Equity/Interests | Level 1
Schedule of Investments [Line Items]
Fair Value	1,514	1,217
Common Equity/Interests | Level 3
Schedule of Investments [Line Items]
Fair Value	157,406	152,127
Warrants - Warrants
Schedule of Investments [Line Items]
Investment cost	965	389
Fair Value	258	199
Warrants - Warrants | Level 3
Schedule of Investments [Line Items]
Fair Value	$ 258	$ 199