Fair Value Measurements - Significant Unobservable Inputs of the Company’s Level 3 Financial Instruments (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 48,413,196	$ 48,908,608
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	41,086,163	39,746,981
Level 3 | First lien debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	38,898,776	37,543,544
Level 3 | First lien debt | Yield analysis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value		36,766,038
Level 3 | First lien debt | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	38,306,657
Level 3 | First lien debt | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	321,297	759,391
Level 3 | First lien debt | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	20,925	$ 18,115
Level 3 | First lien debt | Transaction Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 249,897
Level 3 | First lien debt | Low | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.0639	0.0683
Level 3 | First lien debt | Low | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	93	71
Level 3 | First lien debt | Low | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	5	7
Level 3 | First lien debt | High | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.2806	0.1984
Level 3 | First lien debt | High | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	100.13	105.6
Level 3 | First lien debt | High | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	5	7
Level 3 | First lien debt | Weighted Average | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.1074	0.0993
Level 3 | First lien debt | Weighted Average | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	97.74	91.85
Level 3 | First lien debt | Weighted Average | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	5	7
Level 3 | Second lien debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 1,058,842	$ 1,152,723
Level 3 | Second lien debt | Yield analysis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	899,700	906,837
Level 3 | Second lien debt | Market quotation and performance multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 159,142	$ 245,886
Level 3 | Second lien debt | Low | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.1050	0.1042
Level 3 | Second lien debt | Low | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	89.5	61.5
Level 3 | Second lien debt | High | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.1642	0.1533
Level 3 | Second lien debt | High | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	96	100.5
Level 3 | Second lien debt | Weighted Average | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.1208	0.1185
Level 3 | Second lien debt | Weighted Average | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	92.89	87.36
Level 3 | Structured Finance Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 321,468	$ 293,335
Level 3 | Structured Finance Investments | Market quotation and performance multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 321,468	$ 293,335
Level 3 | Structured Finance Investments | Low | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	86.63	81.96
Level 3 | Structured Finance Investments | High | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	101.5	92.96
Level 3 | Structured Finance Investments | Weighted Average | Market quotation and performance multiple | Quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	96.06	88.84
Level 3 | Equity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 807,077	$ 757,379
Level 3 | Equity | Yield analysis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	381,082	274,199
Level 3 | Equity | Market quotation and performance multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	222,375	261,893
Level 3 | Equity | Option pricing model
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	21,526	48,957
Level 3 | Equity | Asset recoverability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	181,200	$ 172,330
Level 3 | Equity | Transaction Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 894
Level 3 | Equity | Low | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.0975	0.1131
Level 3 | Equity | Low | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	5	5.5
Level 3 | Equity | Low | Option pricing model | Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.3200	0.3000
Level 3 | Equity | Low | Asset recoverability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1.0000	1.0000
Level 3 | Equity | High | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.1598	0.1495
Level 3 | Equity | High | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	31	29
Level 3 | Equity | High | Option pricing model | Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.3200	0.5000
Level 3 | Equity | High | Asset recoverability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1.0000	1.0000
Level 3 | Equity | Weighted Average | Yield analysis | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.1335	0.1276
Level 3 | Equity | Weighted Average | Market quotation and performance multiple | Market multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	20.23	17.21
Level 3 | Equity | Weighted Average | Option pricing model | Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.3200	0.4443
Level 3 | Equity | Weighted Average | Asset recoverability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1.0000	1.0000