Forward Currency Contracts - Schedule of Realized and Unrealized Gain (Loss) on Forward Currency Contract (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Open Forward Foreign Currency Contract [Line Items]
Realized gain (loss) on forward currency contracts recognized in income	$ 1,080	$ 0	$ 0
Change in unrealized appreciation (depreciation) on forward currency contracts recognized in income	32,243	1,154	(949)
Foreign exchange
Open Forward Foreign Currency Contract [Line Items]
Realized gain (loss) on forward currency contracts recognized in income	1,080	0	0
Change in unrealized appreciation (depreciation) on forward currency contracts recognized in income	$ 32,243	$ 1,154	$ (949)