Fair Value of Financial Instruments - Fair Value Measurements of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity and other investments	$ 150,179	$ 167,685
Structured credit investments	53,996	51,426
Total investments at fair value	3,113,277	2,787,925
Interest rate swaps	(55,943)	(55,314)
Total	3,057,334	2,732,611
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity and other investments	6,088	7,498
Total investments at fair value	6,088	7,498
Total	6,088	7,498
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity and other investments	10,728	13,128
Structured credit investments	53,996	51,426
Total investments at fair value	66,573	86,489
Interest rate swaps	(55,943)	(55,314)
Total	10,630	31,175
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity and other investments	133,363	147,059
Total investments at fair value	3,040,616	2,693,938
Total	3,040,616	2,693,938
First-lien Debt Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt investments	2,832,772	2,517,894
First-lien Debt Investments | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt investments	1,726	21,935
First-lien Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [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 [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 [Line Items]
Debt investments	39,940	40,762
Mezzanine Debt Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt investments	36,390	10,158
Mezzanine Debt Investments | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt investments	123
Mezzanine Debt Investments | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt investments	$ 36,267	$ 10,158