v3.26.1
Fair Value of Financial Instruments - Reconciliation of Investments Measured at Fair Value Using Significant Unobservable Inputs Level 3 (Details) - Level 3 - USD ($)
$ in Thousands
 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning balance $ 1,087,964 $ 1,152,369
Net realized gain (loss) 58,503 (30,212)
Net change in unrealized appreciation (depreciation) (54,126) 35,843
Purchases, PIK interest, net discount accretion and non-cash exchanges 228,664 463,214
Sales, repayments and non-cash exchanges (386,398) (616,822)
Transfers in/out of Level 3 0 0
Ending balance 934,607 1,004,392
Net change in unrealized appreciation reported within the net change in unrealized appreciation on investments in our consolidated statements operations attributable to our Level 3 assets still held at the reporting date 6,639 18,186
Debt Investments    
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning balance 801,754 916,796
Net realized gain (loss) (8,511) (29,436)
Net change in unrealized appreciation (depreciation) (2,977) 9,063
Purchases, PIK interest, net discount accretion and non-cash exchanges 221,892 455,557
Sales, repayments and non-cash exchanges (308,557) (614,289)
Transfers in/out of Level 3 0 0
Ending balance 703,601 737,691
Net change in unrealized appreciation reported within the net change in unrealized appreciation on investments in our consolidated statements operations attributable to our Level 3 assets still held at the reporting date (11,679) (7,561)
Equity Investments    
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning balance 286,210 235,573
Net realized gain (loss) 67,014 (776)
Net change in unrealized appreciation (depreciation) (51,149) 26,780
Purchases, PIK interest, net discount accretion and non-cash exchanges 6,772 7,657
Sales, repayments and non-cash exchanges (77,841) (2,533)
Transfers in/out of Level 3 0 0
Ending balance 231,006 266,701
Net change in unrealized appreciation reported within the net change in unrealized appreciation on investments in our consolidated statements operations attributable to our Level 3 assets still held at the reporting date $ 18,318 $ 25,747