v3.26.1
Fair Value Measurements - Schedule of Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($)
$ in Thousands
9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, beginning of period $ 2,209,174 $ 1,311,001
Fundings of (proceeds from) revolving loans, net 15,684 5,697
Fundings of investments 643,075 636,176
PIK interest and non-cash dividends 12,101 7,360
Proceeds from non-cash dividends (111) (170)
Proceeds from principal payments and sales of portfolio investments (179,756) (81,694)
Fair value, end of period 2,667,489 1,895,482
Debt Investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, beginning of period 2,174,044 1,294,931
Fundings of (proceeds from) revolving loans, net 15,684 5,697
Fundings of investments 626,595 623,803
PIK interest and non-cash dividends 11,390 6,973
Proceeds from non-cash dividends 0 0
Proceeds from principal payments and sales of portfolio investments (169,194) (81,345)
Fair value, end of period 2,626,368 1,864,914
Equity Investments    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value, beginning of period 35,130 16,070
Fundings of (proceeds from) revolving loans, net 0 0
Fundings of investments 16,480 12,373
PIK interest and non-cash dividends 711 387
Proceeds from non-cash dividends (111) (170)
Proceeds from principal payments and sales of portfolio investments (10,562) (349)
Fair value, end of period 41,121 30,568
Location, Statement of Income, Balance [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss    
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 $ 1,319  
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Investments  
Location, Statement of Income, Balance [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | Debt 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 $ 64  
Location, Statement of Income, Balance [Axis]: us-gaap:DebtAndEquitySecuritiesRealizedGainLoss | Equity 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 1,255  
Location, Statement of Income, Balance [Axis]: us-gaap:DebtAndEquitySecuritiesUnrealizedGainLoss    
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 $ (35,756) $ 4,060
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Investments Investments
Location, Statement of Income, Balance [Axis]: us-gaap:DebtAndEquitySecuritiesUnrealizedGainLoss | Debt 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 $ (33,984) $ 1,803
Location, Statement of Income, Balance [Axis]: us-gaap:DebtAndEquitySecuritiesUnrealizedGainLoss | Equity 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 (1,772) 2,257
Location, Statement of Income, Balance [Axis]: us-gaap:ForeignCurrencyTransactionGainLossRealized    
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 $ 823 $ 105
Fair value, asset, recurring basis, unobservable input reconciliation, gain (loss), statement of income or comprehensive income [Extensible Enumeration] Foreign currency transactions Foreign currency transactions
Location, Statement of Income, Balance [Axis]: us-gaap:ForeignCurrencyTransactionGainLossRealized | Debt 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 $ 823 $ 105
Location, Statement of Income, Balance [Axis]: us-gaap:ForeignCurrencyTransactionGainLossRealized | Equity 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 0 0
Location, Statement of Income, Balance [Axis]: us-gaap:GrossInvestmentIncomeOperating    
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 $ 5,171 $ 3,722
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
Location, Statement of Income, Balance [Axis]: us-gaap:GrossInvestmentIncomeOperating | Debt 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 $ 5,171 $ 3,722
Location, Statement of Income, Balance [Axis]: us-gaap:GrossInvestmentIncomeOperating | Equity 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 0 0
Location, Statement of Income, Balance [Axis]: us-gaap:UnrealizedGainLossOnDerivatives    
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 $ (4,235) $ 9,225
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
Location, Statement of Income, Balance [Axis]: us-gaap:UnrealizedGainLossOnDerivatives | Debt 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 $ (4,225) $ 9,225
Location, Statement of Income, Balance [Axis]: us-gaap:UnrealizedGainLossOnDerivatives | Equity 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 $ (10) $ 0