v3.25.2
Fair Value Measurements - Fair Value Measurement Inputs and Valuation Techniques (Details)
$ in Thousands
Jun. 30, 2025
USD ($)
Sep. 30, 2024
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 8,961,549 [1] $ 8,235,411 [2]
Level 3 | Senior secured loans    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value 480,592 502,386
Level 3 | Senior secured loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 8,249 $ 2,807
Level 3 | Senior secured loans | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.070 0.065
Level 3 | Senior secured loans | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 3.7 1.5
Level 3 | Senior secured loans | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.155 0.203
Level 3 | Senior secured loans | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 23.9 24.0
Level 3 | Senior secured loans | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.092 0.105
Level 3 | Senior secured loans | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 13.9 12.3
Level 3 | One stop loans    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value   $ 7,057,577
Level 3 | One stop loans | Yield analysis    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 7,785,066  
Level 3 | One stop loans | Broker/dealer bids or quotes    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value   52,681
Level 3 | One stop loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value 87,147 64,786
Level 3 | One stop loans | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value 6,840,170 6,036,312
Level 3 | One stop loans | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 944,896 $ 1,021,265
Level 3 | One stop loans | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.038 0.043
Level 3 | One stop loans | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 3.4 2.8
Level 3 | One stop loans | Minimum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 1.4 1.0
Level 3 | One stop loans | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.263 0.210
Level 3 | One stop loans | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 36.0 53.2
Level 3 | One stop loans | Maximum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 18.0 18.0
Level 3 | One stop loans | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.092 0.099
Level 3 | One stop loans | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 15.8 16.0
Level 3 | One stop loans | Weighted Average | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 8.3 7.9
Level 3 | Subordinated debt and second lien loans    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 66,044 $ 44,229
Level 3 | Subordinated debt and second lien loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value 360 $ 435
Level 3 | Subordinated debt and second lien loans | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value 65,990  
Level 3 | Subordinated debt and second lien loans | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 54  
Investment company, investment owned, measurement input 8.5  
Level 3 | Subordinated debt and second lien loans | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.088 0.100
Level 3 | Subordinated debt and second lien loans | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 5.0 5.5
Level 3 | Subordinated debt and second lien loans | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.163 0.155
Level 3 | Subordinated debt and second lien loans | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 24.0 24.0
Level 3 | Subordinated debt and second lien loans | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 0.112 0.133
Level 3 | Subordinated debt and second lien loans | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 15.3 16.0
Level 3 | Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 629,847 $ 578,420
Level 3 | Equity | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value 550,405 505,597
Level 3 | Equity | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments, at fair value $ 79,442 $ 72,823
Level 3 | Equity | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 4.7 5.5
Level 3 | Equity | Minimum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 1.3 1.2
Level 3 | Equity | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 29.1 53.2
Level 3 | Equity | Maximum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 18.0 18.0
Level 3 | Equity | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 16.3 18.2
Level 3 | Equity | Weighted Average | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment company, investment owned, measurement input 8.5 8.1
[1] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See Note 6.
[2] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See Note 6.