v3.25.0.1
Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2024
Sep. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value $ 8,685,231 [1] $ 8,235,411 [2]
Money market funds 153,214 213,101
Forward currency contracts 17,292 5,695
Interest rate swaps 2,691 31,486
Total assets, at fair value: 8,858,428 8,485,693
Forward currency contracts (255) (7,691)
Interest rate swaps (10,148)  
Total liabilities, at fair value: (10,403) (7,691)
Level 1    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Money market funds 153,214 213,101
Forward currency contracts 0 0
Interest rate swaps 0
Total assets, at fair value: 153,316 213,219
Forward currency contracts 0 0
Interest rate swaps 0  
Total liabilities, at fair value: 0 0
Level 2    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Money market funds 0 0
Forward currency contracts 17,292 5,695
Interest rate swaps 2,691 31,486
Total assets, at fair value: 19,983 37,181
Forward currency contracts (255) (7,691)
Interest rate swaps (10,148)  
Total liabilities, at fair value: (10,403) (7,691)
Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Money market funds 0 0
Forward currency contracts 0
Interest rate swaps 0
Total assets, at fair value: 8,685,129 8,235,293
Forward currency contracts 0 0
Interest rate swaps 0  
Total liabilities, at fair value: 0 0
Debt investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 8,076,256 7,656,873
Debt investments | Level 1    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 0 0
Debt investments | Level 2    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 0 0
Debt investments | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 8,076,256 7,656,873
Equity investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 608,975 578,538
Equity investments | Level 1    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 102 118
Equity investments | Level 2    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value 0 0
Equity investments | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Investments, at fair value $ 608,873 $ 578,420
[1] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See “Note 6. Fair Value Measurements”.
[2] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See “Note 6. Fair Value Measurements”.