Income Taxes - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance, beginning of year	$ 22,283	$ 52,085	$ 205,423
Net release of valuation allowance	0	0	(134,235)
Net decrease in deferred tax assets with a full valuation allowance	(588)	(29,802)	(19,103)
Valuation allowance, end of year	$ 21,695	$ 22,283	$ 52,085