Summary of Significant Accounting Policies - ASC 606 - Impact - Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 179,368	$ 142,599
Cost of Revenue	107,287	88,340
Gross profit	72,081	54,259
Operating expenses	66,748	49,334
Operating income	5,333	$ 4,925
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	(401)
Cost of Revenue	(512)
Gross profit	111
Operating expenses	204
Operating income	(93)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	179,769
Cost of Revenue	107,799
Gross profit	71,970
Operating expenses	66,544
Operating income	$ 5,426