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 $ 2,729,010 $ 1,917,839
Net realized gain (loss) $ (6,067) $ 23,197
Net change in unrealized depreciation/appreciation Gain (Loss) on Investments Gain (Loss) on Investments
Net change in unrealized depreciation/appreciation $ 3,744 $ (30,449)
Purchases, PIK interest, net discount accretion and non-cash exchanges 401,956 888,869
Sales, repayments and non-cash exchanges (636,357) (523,668)
Ending Balance 2,492,286 2,275,788
Net change in unrealized depreciation 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. $ (651) $ (6,656)
Net change in unrealized appreciation (depreciation) reported Net Change in Unrealized Appreciation (Depreciation) Net Change in Unrealized Appreciation (Depreciation)
First lien    
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance $ 2,513,631 $ 1,746,697
Net realized gain (loss) (8,012) 879
Net change in unrealized depreciation/appreciation (20,609) (18,852)
Purchases, PIK interest, net discount accretion and non-cash exchanges 394,789 870,397
Sales, repayments and non-cash exchanges (627,671) (498,948)
Ending Balance 2,252,128 2,100,173
Net change in unrealized depreciation 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. (25,226) (14,454)
Second Lien, Subordinated Debt and Equity Investments    
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance 215,379 171,142
Net realized gain (loss) 1,945 22,318
Net change in unrealized depreciation/appreciation (24,353) (11,597)
Purchases, PIK interest, net discount accretion and non-cash exchanges 7,167 18,472
Sales, repayments and non-cash exchanges (8,686) (24,720)
Ending Balance 240,158 175,615
Net change in unrealized depreciation 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. $ 24,575 $ 7,798