v3.25.2
Portfolio Investments - Schedule of Significant Unobservable Inputs for Level 3 Investments (Details)
$ in Thousands
Jun. 30, 2025
USD ($)
Sep. 30, 2024
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 2,809,377 $ 3,021,279
Senior secured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 2,343,411 2,574,937
Subordinated debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 138,122 109,921
Debt investments in the JVs    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 159,720 161,552
Level 3    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 2,485,322 2,723,732
Level 3 | Senior secured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 2,076,845 2,320,310
Level 3 | Senior secured debt | Market Yield | Market Yield    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 1,988,077 $ 2,044,221
Level 3 | Senior secured debt | Market Yield | Market Yield | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.070 0.057
Level 3 | Senior secured debt | Market Yield | Market Yield | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.400 0.310
Level 3 | Senior secured debt | Market Yield | Market Yield | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.112 0.120
Level 3 | Senior secured debt | Enterprise Value | Revenue Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 44,161 $ 52,857
Level 3 | Senior secured debt | Enterprise Value | Revenue Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.5 2.0
Level 3 | Senior secured debt | Enterprise Value | Revenue Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 5.5 5.5
Level 3 | Senior secured debt | Enterprise Value | Revenue Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 2.8 3.7
Level 3 | Senior secured debt | Enterprise Value | EBITDA Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 31,985 $ 26,927
Level 3 | Senior secured debt | Enterprise Value | EBITDA Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 2.6 4.5
Level 3 | Senior secured debt | Enterprise Value | EBITDA Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 8.2 7.5
Level 3 | Senior secured debt | Enterprise Value | EBITDA Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 6.7 5.7
Level 3 | Senior secured debt | Transaction Precedent | Transaction Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 12,622 $ 33,272
Level 3 | Senior secured debt | Broker Quotations | Broker Quoted Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value   163,033
Level 3 | Subordinated debt | Market Yield | Market Yield    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 97,778 $ 93,794
Level 3 | Subordinated debt | Market Yield | Market Yield | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.050 0.050
Level 3 | Subordinated debt | Market Yield | Market Yield | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.120 0.450
Level 3 | Subordinated debt | Market Yield | Market Yield | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.093 0.101
Level 3 | Debt investments in the JVs | Enterprise Value    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 159,720 $ 161,552
Level 3 | Preferred & Common Equity | Enterprise Value | Revenue Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 64,170 $ 80,720
Level 3 | Preferred & Common Equity | Enterprise Value | Revenue Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.3 0.3
Level 3 | Preferred & Common Equity | Enterprise Value | Revenue Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 5.5 7.2
Level 3 | Preferred & Common Equity | Enterprise Value | Revenue Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 0.6 2.0
Level 3 | Preferred & Common Equity | Enterprise Value | EBITDA Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 85,313 $ 66,106
Level 3 | Preferred & Common Equity | Enterprise Value | EBITDA Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 2.6 2.9
Level 3 | Preferred & Common Equity | Enterprise Value | EBITDA Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 17.4 15.0
Level 3 | Preferred & Common Equity | Enterprise Value | EBITDA Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 10.7 10.2
Level 3 | Preferred & Common Equity | Enterprise Value | Asset Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 1,496 $ 1,250
Level 3 | Preferred & Common Equity | Enterprise Value | Asset Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 1.4 1.0
Level 3 | Preferred & Common Equity | Enterprise Value | Asset Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 1.6 1.4
Level 3 | Preferred & Common Equity | Enterprise Value | Asset Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value, measurement input 1.5 1.4