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	Sep. 30, 2024	Dec. 31, 2023
First-lien Debt Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	$ 5,611,439	$ 2,850,885
First-lien Debt Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	5,428,702	2,848,805
Asset Valuation Waterfall | First-lien Debt Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt investments	64,800	77,900
Black Scholes Model | Equity and Other Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investment	7,800	4,600
Cost Model | Equity and Other Investments | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity investment	$ 235,800	$ 19,200