Income Taxes - Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized Tax Benefits - beginning balance	$ 27,716	$ 26,203	$ 23,719
Decrease resulting from prior period tax positions	(26)	(923)
Increase resulting from prior period tax positions			22
Increase resulting from current period tax positions	3,231	2,436	2,462
Unrecognized tax benefits - ending balance	30,921	27,716	26,203
Unrecognized tax benefits, period increase	30,900
Less: deferred federal and state income tax benefits	(6,493)	(5,820)	(5,503)
Total unrecognized tax benefits that, if recognized, would impact the effective income tax rate as of the end of the year	$ 24,428	$ 21,896	$ 20,700