Income Taxes - Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 23,719	$ 20,298	$ 17,069	$ 26,203	$ 23,719	$ 20,298
Decrease resulting from prior period tax positions		(366)	(290)
Increase resulting from prior period tax positions	22
Increase resulting from current period tax positions	2,462	3,787	3,519
Unrecognized tax benefits - ending balance	$ 23,719	$ 20,298	$ 17,069
Less: deferred federal and state income tax benefits				(5,503)	(8,302)	(7,104)
Total unrecognized tax benefits that, if recognized, would impact the effective income tax rate as of the end of the year				$ 20,700	$ 15,417	$ 13,194