v3.26.1
Fair Value Measurements - Schedule of Fair Value, Assets Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 2,667,489 [1] $ 2,209,174 [2]
Money market funds 39,950 46,041
Forward currency contracts 51  
Total assets, at fair value: 2,707,490 2,255,215
Forward currency contracts (554) (864)
Total liabilities, at fair value: (554) (864)
Debt Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 2,626,368 2,174,044
Equity Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 41,121 35,130
Level 1    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Money market funds 39,950 46,041
Forward currency contracts 0  
Total assets, at fair value: 39,950 46,041
Forward currency contracts 0 0
Total liabilities, at fair value: 0 0
Level 1 | Debt Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 0 0
Level 1 | Equity Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 0 0
Level 2    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Money market funds 0 0
Forward currency contracts 51  
Total assets, at fair value: 51 0
Forward currency contracts (554) (864)
Total liabilities, at fair value: (554) (864)
Level 2 | Debt Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 0 0
Level 2 | Equity Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 0 0
Level 3    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Money market funds 0 0
Forward currency contracts 0  
Total assets, at fair value: 2,667,489 2,209,174
Forward currency contracts 0 0
Total liabilities, at fair value: 0 0
Level 3 | Debt Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 2,626,368 2,174,044
Level 3 | Equity Investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 41,121 $ 35,130
[1] The fair values of investments were valued using significant unobservable inputs, unless otherwise noted. See Note 7. 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 7. The fair value of loan investments may include the impact of the unfunded commitment being valued below par.