Fair Value Measurements - Unobservable Inputs (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 9,500,000	$ 9,617,248
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	9,318,628	9,472,796
First lien debt | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	9,166,292	9,275,511
First lien debt | Yield analysis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	9,024,693	9,037,133
First lien debt | Market approach | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	1,023	$ 238,378
First lien debt | Transaction price | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 140,576
First lien debt | Low | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0639	0.0683
First lien debt | Low | Market approach | Level 3 | Broker quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	94.81	82.00
First lien debt | High | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.2806	0.1984
First lien debt | High | Market approach | Level 3 | Broker quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	94.81	96.75
First lien debt | Weighted Average | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1100	0.1013
First lien debt | Weighted Average | Market approach | Level 3 | Broker quoted price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	94.81	94.19
Second lien debt | Yield analysis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 40,715	$ 46,336
Second lien debt | Low | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1077	0.1043
Second lien debt | High | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1481	0.1425
Second lien debt | Weighted Average | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1281	0.1260
Investments in equity | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 111,621	$ 150,949
Investments in equity | Yield analysis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	39,506	22,686
Investments in equity | Market approach | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	60,107	105,782
Investments in equity | Option pricing model | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	11,591	$ 22,481
Investments in equity | Transaction price | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 417
Investments in equity | Low | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0975	0.1131
Investments in equity | Low | Market approach | Level 3 | Performance Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.06	5.50
Investments in equity | Low | Option pricing model | Level 3 | Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.3200	0.3000
Investments in equity | High | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1598	0.1375
Investments in equity | High | Market approach | Level 3 | Performance Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.31	29.00
Investments in equity | High | Option pricing model | Level 3 | Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.3200	0.5000
Investments in equity | Weighted Average | Yield analysis | Level 3 | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1296	0.1274
Investments in equity | Weighted Average | Market approach | Level 3 | Performance Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	11.08	13.41
Investments in equity | Weighted Average | Option pricing model | Level 3 | Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.3200	0.4346