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	Jun. 30, 2025	Dec. 31, 2024
First-lien Debt Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	$ 7,103,934	$ 6,871,809
First-lien Debt Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	6,838,709	6,728,411
Asset Valuation Waterfall | First-lien Debt Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	54,100	226,400
Black Scholes Model | Equity and Other Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investment		8,300
Cost Model | Equity and Other Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investment	$ 52,800	$ 49,100