Income Taxes - Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, period increase	$ 32,800
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized Tax Benefits - beginning balance	30,921	$ 27,716	$ 26,203
Increase (decrease) resulting from prior period tax positions		(26)	(923)
Increase resulting from current period tax positions	1,200	3,231	2,436
Unrecognized tax benefits - ending balance	32,792	30,921	27,716
Increase resulting from prior period tax positions	671
Less: deferred federal and state income tax benefits	(6,886)	(6,493)	(5,820)
Total unrecognized tax benefits that, if recognized, would impact the effective income tax rate as of the end of the year	$ 25,906	$ 24,428	$ 21,896