v3.26.1
Fair Value Measurements - Schedule of Quantitative Information about Level 3 Fair Value Measurements (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 8,196,353 [1] $ 8,769,389 [2]
Level 3 | Senior secured loans    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value   442,477
Level 3 | Senior secured loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 6,199 $ 67
Level 3 | Senior secured loans | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.085 0.073
Level 3 | Senior secured loans | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 3.5 3.5
Level 3 | Senior secured loans | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.155 0.170
Level 3 | Senior secured loans | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 32.3 26.3
Level 3 | Senior secured loans | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.102 0.091
Level 3 | Senior secured loans | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 13.6 14.2
Level 3 | One stop loans | Yield analysis    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 7,149,784 $ 7,603,780
Level 3 | One stop loans | Broker/dealer bids or quotes    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 12,678 12,029
Level 3 | One stop loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 65,490 46,465
Level 3 | One stop loans | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 6,332,555 6,600,901
Level 3 | One stop loans | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 817,229 $ 1,002,879
Level 3 | One stop loans | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.050 0.038
Level 3 | One stop loans | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 4.2 3.9
Level 3 | One stop loans | Minimum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.8 1.4
Level 3 | One stop loans | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.335 0.205
Level 3 | One stop loans | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 32.3 39.2
Level 3 | One stop loans | Maximum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 14.0 15.0
Level 3 | One stop loans | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.102 0.091
Level 3 | One stop loans | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 14.5 15.7
Level 3 | One stop loans | Weighted Average | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 7.0 8.0
Level 3 | Subordinated debt and second lien loans    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 59,048 $ 64,821
Level 3 | Subordinated debt and second lien loans | Market comparable companies    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value   $ 132
Level 3 | Subordinated debt and second lien loans | Minimum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.105 0.088
Level 3 | Subordinated debt and second lien loans | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 4.2 4.0
Level 3 | Subordinated debt and second lien loans | Maximum | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.140 0.220
Level 3 | Subordinated debt and second lien loans | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 21.0 24.0
Level 3 | Subordinated debt and second lien loans | Weighted Average | Market interest rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.124 0.111
Level 3 | Subordinated debt and second lien loans | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 14.5 15.5
Level 3 | Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 583,711 $ 646,282
Level 3 | Equity | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 519,746 563,467
Level 3 | Equity | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 63,965 $ 82,815
Level 3 | Equity | Minimum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 4.2 4.0
Level 3 | Equity | Minimum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 0.2 1.4
Level 3 | Equity | Maximum | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 32.3 39.2
Level 3 | Equity | Maximum | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 18.8 21.3
Level 3 | Equity | Weighted Average | EBITDA multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 14.1 16.4
Level 3 | Equity | Weighted Average | Revenue multiples    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Range (Weighted Average) 8.2 8.8
[1] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. 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 noted otherwise. See Note 6. The fair value of loan investments may include the impact of the unfunded commitment being valued below par.