Investments - Schedule of Investments Excluding Investments in Money Market Funds (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Schedule Of Investments [Line Items]
Cost	$ 3,602,647	$ 3,573,791
Fair Value	3,440,114	3,414,329
1st Lien/Senior Secured Debt
Schedule Of Investments [Line Items]
Cost	3,261,817	3,209,938
Fair Value	3,162,664	3,107,469
1st Lien/Last-Out Unitranche
Schedule Of Investments [Line Items]
Cost	161,071	148,067
Fair Value	158,514	144,743
2nd Lien/Senior Secured Debt
Schedule Of Investments [Line Items]
Cost	50,658	84,626
Fair Value	33,636	66,562
Unsecured Debt
Schedule Of Investments [Line Items]
Cost	29,176	27,930
Fair Value	20,550	27,314
Preferred Stock
Schedule Of Investments [Line Items]
Cost	44,322	44,198
Fair Value	38,002	37,296
Common Stock
Schedule Of Investments [Line Items]
Cost	53,754	57,183
Fair Value	26,501	30,701
Warrants
Schedule Of Investments [Line Items]
Cost	1,849	1,849
Fair Value	$ 247	$ 244