Fair Value of Financial Instruments - Fair Value of Level 3 Investments at Fair Value Significant Unobservable Inputs Used in Valuations (Parenthetical) (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
First-lien Debt Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	$ 6,864,996	$ 6,871,809
First-lien Debt Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	6,686,427	6,728,411
Asset Valuation Waterfall | First-lien Debt Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	62,500	226,400
Black Scholes Model | Equity and Other Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investment	10,300	8,300
Cost Model | Equity and Other Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investment	$ 49,700	$ 49,100