v3.25.4
Fair Value of Financial Instruments - Reconciliation of Investments Measured at Fair Value Using Significant Unobservable Inputs Level 3 (Details) - Level 3 - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance $ 1,152,369 $ 927,328
Net realized gain (loss) (52,458) (33,081)
Net change in unrealized appreciation (depreciation) 55,679 30,616
Purchases, PIK interest, net discount accretion and non-cash exchanges 742,796 786,046
Sales, repayments and non-cash exchanges (810,422) (558,540)
Ending Balance 1,087,964 1,152,369
Net change in unrealized appreciation reported within the net change in unrealized depreciation on investments in our Consolidated Statements of Operations attributable to our Level 3 assets still held at the reporting date. 39,086 4,328
Debt Investments    
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance 916,796 764,275
Net realized gain (loss) (45,658) (23,028)
Net change in unrealized appreciation (depreciation) (9,159) (5,374)
Purchases, PIK interest, net discount accretion and non-cash exchanges 726,966 726,526
Sales, repayments and non-cash exchanges (805,509) (545,603)
Ending Balance 801,754 916,796
Net change in unrealized appreciation reported within the net change in unrealized depreciation on investments in our Consolidated Statements of Operations attributable to our Level 3 assets still held at the reporting date. (1,219) (21,133)
Equity Investments    
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance 235,573 163,053
Net realized gain (loss) (6,800) (10,053)
Net change in unrealized appreciation (depreciation) 46,520 35,990
Purchases, PIK interest, net discount accretion and non-cash exchanges 15,830 59,520
Sales, repayments and non-cash exchanges (4,913) (12,937)
Ending Balance 286,210 235,573
Net change in unrealized appreciation reported within the net change in unrealized depreciation on investments in our Consolidated Statements of Operations attributable to our Level 3 assets still held at the reporting date. $ 40,305 $ 25,461