Fair Value of Financial Instruments - Reconciliation of Liabilities Measured at Fair Value Using Significant Unobservable Inputs Level 3 (Details) - Level 3 - Long-Term Credit Facility - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2025	Sep. 30, 2024
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 460,361	$ 206,940
Net change in unrealized (depreciation) appreciation included in earnings		116	4,385
Borrowings	[1]	207,000	524,036
Repayments	[1]	(242,000)	(275,000)
Ending Balance		$ 425,477	$ 460,361

[1] Excludes temporary draws.