Income Taxes - Summary of Changes in Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Valuation Allowance [Line Items]
Balance at beginning of period	$ 5,973,000	$ 5,853,000	$ 5,518,000
Valuation allowance, deferred tax asset, increase (decrease), amount	121,000	27,000
Balance at end of period	6,378,000	5,973,000	5,853,000
Allowance provision for new operating and other loss carryforwards
Valuation Allowance [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	573,000	325,000	505,000
Allowance benefits
Valuation Allowance [Line Items]
Valuation allowance, deferred tax asset, increase (decrease), amount	$ (168,000)	$ (205,000)	$ (170,000)