Summary of Significant Accounting Policies - ASC 606 - Impact - Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 198,390	$ 179,368	$ 156,952	$ 377,757	$ 299,551
Cost of revenue	117,874	$ 107,287	94,566	225,161	182,906
Gross profit	80,516		62,386	152,596	116,645
Operating expenses	66,844		52,065	133,592	101,399
Operating income	13,672		$ 10,321	19,004	$ 15,246
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	(1,165)			(1,566)
Cost of revenue	(498)			(1,010)
Gross profit	(667)			(556)
Operating expenses	193			397
Operating income	(860)			(953)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	199,555			379,323
Cost of revenue	118,372			226,171
Gross profit	81,183			153,152
Operating expenses	66,651			133,195
Operating income	$ 14,532			$ 19,957

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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