Fair Value of Financial Instruments - Fair Value of Level 3 Investments at Fair Value and Significant Unobservable Inputs Used in Valuations (Parenthetical) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
First-lien Debt Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	$ 2,832,772	$ 2,517,894
First-lien Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	2,831,046	2,495,959
Second-lien Debt Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	39,940	40,762
Second-lien Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	39,940	40,762
Mezzanine Debt Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	36,390	10,158
Mezzanine Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	36,267	10,158
Asset Valuation Waterfall | First-lien Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	20,600	21,000
Asset Valuation Waterfall | Second-lien Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	34,600
Asset Valuation Waterfall | Mezzanine Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Debt investments	100	100
Asset Valuation Waterfall | Equity and Other Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Equity investment	10,300	38,400
Black Scholes Model | Equity and Other Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Equity investment	2,100	7,500
Discounted Cash Flow Model | Equity and Other Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Equity investment	$ 14,900	$ 13,100