Income Taxes - Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized Tax Benefits - beginning balance	$ 26,203	$ 23,719	$ 20,298
Decrease resulting from prior period tax positions	923		366
Increase resulting from prior period tax positions		(22)
Increase resulting from current period tax positions	2,436	2,462	3,787
Unrecognized tax benefits - ending balance	27,716	26,203	23,719
Unrecognized tax benefits, period increase	27,700
Less: deferred federal and state income tax benefits	(5,820)	(5,503)	(8,302)
Total unrecognized tax benefits that, if recognized, would impact the effective income tax rate as of the end of the year	$ 21,896	$ 20,700	$ 15,417