v3.26.1
Fair Value Measurements - Schedule of Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, beginning of year $ 1,311,001 $ 318,915
Fundings of (proceeds from) revolving loans, net 5,121 2,253
Fundings of investments 1,004,018 999,116
PIK interest and non-cash dividends 10,114 6,467
Proceeds from non-cash dividends (208)  
Proceeds from principal payments and sales of portfolio investments (139,651) (36,279)
Fair value, end of year 2,209,174 1,311,001
Net change in unrealized appreciation (depreciation) on investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings $ 5,293 $ 14,348
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Investments Investments
Net translation of investments in foreign currencies    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings $ 7,944 $ 3,043
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Translation of assets and liabilities in foreign currencies Translation of assets and liabilities in foreign currencies
Realized gain (loss) on investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings   $ 30
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration]   Investments
Realized gain (loss) on translation of investments in foreign currencies    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings $ 122 $ 30
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Foreign currency transactions Foreign currency transactions
Accretion of discounts and amortization of premiums    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings $ 5,420 $ 3,078
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Gross Investment Income, Operating Gross Investment Income, Operating
Debt Investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, beginning of year $ 1,294,931 $ 313,688
Fundings of (proceeds from) revolving loans, net 5,121 2,253
Fundings of investments 986,577 989,310
PIK interest and non-cash dividends 9,486 6,286
Proceeds from non-cash dividends 0  
Proceeds from principal payments and sales of portfolio investments (136,788) (36,279)
Fair value, end of year 2,174,044 1,294,931
Debt Investments | Net change in unrealized appreciation (depreciation) on investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings 1,227 13,489
Debt Investments | Net translation of investments in foreign currencies    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings 7,948 3,043
Debt Investments | Realized gain (loss) on investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings   33
Debt Investments | Realized gain (loss) on translation of investments in foreign currencies    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings 122 30
Debt Investments | Accretion of discounts and amortization of premiums    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings 5,420 3,078
Equity Investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, beginning of year 16,070 5,227
Fundings of (proceeds from) revolving loans, net 0 0
Fundings of investments 17,441 9,806
PIK interest and non-cash dividends 628 181
Proceeds from non-cash dividends (208)  
Proceeds from principal payments and sales of portfolio investments (2,863) 0
Fair value, end of year 35,130 16,070
Equity Investments | Net change in unrealized appreciation (depreciation) on investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings 4,066 859
Equity Investments | Net translation of investments in foreign currencies    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings (4) 0
Equity Investments | Realized gain (loss) on investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings   (3)
Equity Investments | Realized gain (loss) on translation of investments in foreign currencies    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings 0 0
Equity Investments | Accretion of discounts and amortization of premiums    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, gain (loss) included in earnings $ 0 $ 0