v3.25.2
Investments - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2025
Sep. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Principal $ 8,480,404 $ 7,830,886
Amortized Cost 8,967,518 8,302,913
Fair Value 8,961,549 [1] 8,235,411 [2]
Senior secured    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Principal 487,388 510,503
Amortized Cost 481,388 506,178
Fair Value 480,592 502,386
One stop    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Principal 7,922,217 7,271,543
Amortized Cost 7,818,613 7,216,368
Fair Value 7,785,066 7,110,258
Second lien    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Principal 33,322 18,430
Amortized Cost 31,640 17,125
Fair Value 28,625 14,054
Subordinated debt    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Principal 37,477 30,410
Amortized Cost 36,988 29,943
Fair Value 37,419 30,175
Equity    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Amortized Cost 598,889 533,299
Fair Value $ 629,847 $ 578,538
[1] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See Note 6.
[2] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See Note 6.