Summary of Significant Accounting Policies - ASC 606 - Impact - Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 203,880	$ 179,368	$ 172,363	$ 581,637	$ 471,914
Cost of revenue	120,370	$ 107,287	105,548	345,531	288,453
Gross profit	83,510		66,815	236,106	183,461
Operating expenses	67,087		54,268	200,679	155,667
Operating income	16,423		$ 12,547	35,427	$ 27,794
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	(858)			(2,424)
Cost of revenue	(468)			(1,478)
Gross profit	(390)			(946)
Operating expenses	173			570
Operating income	(563)			(1,516)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	204,738			584,061
Cost of revenue	120,838			347,009
Gross profit	83,900			237,052
Operating expenses	66,914			200,109
Operating income	$ 16,986			$ 36,943