v3.26.1
Fair Value Measurements - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 9,616,525 [1] $ 8,555,251 [2]
Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 99,667 64,837
Level 3    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 8,339,916 6,804,856
Level 3 | Senior secured loans | Yield analysis    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 343,769 $ 358,580
Level 3 | Senior secured loans | Yield analysis | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.085 0.073
Level 3 | Senior secured loans | Yield analysis | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.140 0.125
Level 3 | Senior secured loans | Yield analysis | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.090 0.083
Level 3 | Senior secured loans | Market comparable companies | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 5.5 6.0
Level 3 | Senior secured loans | Market comparable companies | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 20.5 20.0
Level 3 | Senior secured loans | Market comparable companies | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 11.2 13.5
Level 3 | Senior secured loans | Broker quotes    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 105,602 $ 178,937
Level 3 | One stop loans | Yield analysis    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 7,414,204 5,901,144
Level 3 | One stop loans | Yield analysis | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 6,771,664 5,262,911
Level 3 | One stop loans | Yield analysis | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 642,540 $ 638,233
Level 3 | One stop loans | Yield analysis | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.075 0.038
Level 3 | One stop loans | Yield analysis | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.210 0.205
Level 3 | One stop loans | Yield analysis | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.095 0.086
Level 3 | One stop loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 6,732 $ 11,327
Level 3 | One stop loans | Market comparable companies | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 6.8 8.0
Level 3 | One stop loans | Market comparable companies | Minimum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.8 1.8
Level 3 | One stop loans | Market comparable companies | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 29.3 34.4
Level 3 | One stop loans | Market comparable companies | Maximum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 14.0 15.0
Level 3 | One stop loans | Market comparable companies | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 14.6 15.9
Level 3 | One stop loans | Market comparable companies | Weighted Average | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 7.8 8.2
Level 3 | One stop loans | Broker quotes    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 76,611 $ 47,696
Level 3 | Subordinated debt and second lien loans | Yield analysis    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 88,966 $ 92,730
Level 3 | Subordinated debt and second lien loans | Yield analysis | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.105 0.088
Level 3 | Subordinated debt and second lien loans | Yield analysis | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.140 0.150
Level 3 | Subordinated debt and second lien loans | Yield analysis | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.121 0.101
Level 3 | Subordinated debt and second lien loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value   $ 66
Level 3 | Subordinated debt and second lien loans | Market comparable companies | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 13.0 12.5
Level 3 | Subordinated debt and second lien loans | Market comparable companies | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 21.0 24.0
Level 3 | Subordinated debt and second lien loans | Market comparable companies | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 18.1 18.4
Level 3 | Structured finance notes | Broker quotes    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 211,097 $ 147,182
Level 3 | Structured finance notes | Transactional value    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value   13,750
Level 3 | Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 99,667 64,837
Level 3 | Equity | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 99,667 64,837
Level 3 | Equity | Market comparable companies | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 67,851 50,649
Level 3 | Equity | Market comparable companies | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 31,816 $ 14,188
Level 3 | Equity | Market comparable companies | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 5.5 8.0
Level 3 | Equity | Market comparable companies | Minimum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 0.8 1.8
Level 3 | Equity | Market comparable companies | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 26.0 25.5
Level 3 | Equity | Market comparable companies | Maximum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 13.0 11.1
Level 3 | Equity | Market comparable companies | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 16.5 18.2
Level 3 | Equity | Market comparable companies | Weighted Average | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Measurement input 9.0 9.3
[1] The fair values of investments were valued using significant unobservable inputs, unless otherwise noted. See Note 6. The fair value of loan investments may include the impact of the unfunded commitment being valued below par.
[2] The fair values of investments were valued using significant unobservable inputs, unless otherwise noted. See Note 6. The fair value of loan investments may include the impact of the unfunded commitment being valued below par.