Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Tax Credit Carryforward [Line Items]
Federal net operating loss carryforwards	$ 100,300
Federal and state net operating loss carryforwards	177,611	$ 192,981
State net operating loss carryforwards	34,900
Valuation allowance	(29,059)	(39,185)
Pre-tax income required to realize deferred tax assets prior to expiration	927,400
Unrecognized tax benefits	3,358	$ 3,441	$ 3,473	$ 3,494
Federal tax authority
Tax Credit Carryforward [Line Items]
Federal and state net operating loss carryforwards	$ 45,700