Investments - Schedule of Composition of Investment Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Investment cost	$ 2,635,330	$ 2,538,142
Fair Value	2,444,352	2,334,199
Total Cash Equivalents	675	252
Total Cash Equivalents, Fair Value	675	252
Total Investments after Cash Equivalents	2,636,005	2,538,394
Total Investments after Cash Equivalents, Fair Value	2,445,027	2,334,451
Money Market Funds [Member]
Schedule of Investments [Line Items]
Total Cash Equivalents	675	252
Total Cash Equivalents, Fair Value	675	252
Level 1
Schedule of Investments [Line Items]
Fair Value	1,745	1,217
Total Cash Equivalents, Fair Value	675	252
Total Investments after Cash Equivalents, Fair Value	2,420	1,469
Level 1 | Money Market Funds [Member]
Schedule of Investments [Line Items]
Total Cash Equivalents, Fair Value	675	252
Level 2
Schedule of Investments [Line Items]
Fair Value	7,955
Total Investments after Cash Equivalents, Fair Value	7,955
Level 3
Schedule of Investments [Line Items]
Fair Value	2,434,652	2,332,982
Total Investments after Cash Equivalents, Fair Value	2,434,652	2,332,982
First Lien Secured Debt
Schedule of Investments [Line Items]
Investment cost	2,222,375	2,093,887
Fair Value	2,202,813	2,075,031
First Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	2,202,813	2,075,031
Second Lien Secured Debt
Schedule of Investments [Line Items]
Investment cost	15,520	46,274
Fair Value	13,401	31,887
Second Lien Secured Debt | Level 2
Schedule of Investments [Line Items]
Fair Value	7,955
Second Lien Secured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	5,446	31,887
Unsecured Debt
Schedule of Investments [Line Items]
Investment cost	2,672
Fair Value	325
Unsecured Debt | Level 3
Schedule of Investments [Line Items]
Fair Value	325
Structured Products And Other
Schedule of Investments [Line Items]
Investment cost	44,438	44,993
Fair Value	34,705	41,333
Structured Products And Other | Level 3
Schedule of Investments [Line Items]
Fair Value	34,705	41,333
Preferred Equity
Schedule of Investments [Line Items]
Investment cost	25,802	25,685
Fair Value	32,610	32,405
Preferred Equity | Level 3
Schedule of Investments [Line Items]
Fair Value	32,610	32,405
Common Equity/Interests
Schedule of Investments [Line Items]
Investment cost	323,558	326,914
Fair Value	160,328	153,344
Common Equity/Interests | Level 1
Schedule of Investments [Line Items]
Fair Value	1,745	1,217
Common Equity/Interests | Level 3
Schedule of Investments [Line Items]
Fair Value	158,583	152,127
Warrants - Warrants
Schedule of Investments [Line Items]
Investment cost	965	389
Fair Value	170	199
Warrants - Warrants | Level 3
Schedule of Investments [Line Items]
Fair Value	$ 170	$ 199