v3.26.1
Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Assets, at fair value:    
Investments, at fair value $ 8,196,353 [1] $ 8,769,389 [2]
Money market funds 43,572 93,656
Forward currency contracts 10,261 185
Interest rate swaps 3,245 20,408
Total assets, at fair value: 8,253,431 8,883,638
Liabilities, at fair value:    
Forward currency contracts (1,589) (12,798)
Interest rate swaps (9,567) (689)
Total liabilities, at fair value: (11,156) (13,487)
Level 1    
Assets, at fair value:    
Money market funds 43,572 93,656
Forward currency contracts 0 0
Interest rate swaps 0 0
Total assets, at fair value: 43,572 93,656
Liabilities, at fair value:    
Forward currency contracts 0 0
Interest rate swaps 0 0
Total liabilities, at fair value: 0 0
Level 2    
Assets, at fair value:    
Money market funds 0 0
Forward currency contracts 10,261 185
Interest rate swaps 3,245 20,408
Total assets, at fair value: 13,506 20,593
Liabilities, at fair value:    
Forward currency contracts (1,589) (12,798)
Interest rate swaps (9,567) (689)
Total liabilities, at fair value: (11,156) (13,487)
Level 3    
Assets, at fair value:    
Money market funds 0 0
Forward currency contracts 0 0
Interest rate swaps 0 0
Total assets, at fair value: 8,196,353 8,769,389
Liabilities, at fair value:    
Forward currency contracts 0 0
Interest rate swaps 0 0
Total liabilities, at fair value: 0 0
Debt investments    
Assets, at fair value:    
Investments, at fair value 7,612,642 8,123,107
Debt investments | Level 1    
Assets, at fair value:    
Investments, at fair value 0 0
Debt investments | Level 2    
Assets, at fair value:    
Investments, at fair value 0 0
Debt investments | Level 3    
Assets, at fair value:    
Investments, at fair value 7,612,642 8,123,107
Equity investments    
Assets, at fair value:    
Investments, at fair value 583,711 646,282
Equity investments | Level 1    
Assets, at fair value:    
Investments, at fair value 0 0
Equity investments | Level 2    
Assets, at fair value:    
Investments, at fair value 0 0
Equity investments | Level 3    
Assets, at fair value:    
Investments, at fair value $ 583,711 $ 646,282
[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.