Summary of Significant Accounting Policies - ASC 606 - Impact - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Oct. 01, 2018	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	$ 46,332	$ 32,091	$ 31,741
Other assets	20,506	6,777	5,294
Deferred revenue	29,435	28,734	25,884
Accumulated deficit	(586,412)	(994,933)	$ (994,074)
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets		350
Other assets		1,483
Deferred revenue		2,850
Accumulated deficit		$ (859)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	42,294
Other assets	19,686
Deferred revenue	27,390
Accumulated deficit	(589,225)
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]
Prepaid expenses and other current assets	4,038
Other assets	820
Deferred revenue	2,045
Accumulated deficit	$ 2,813