Summary of Significant Accounting Policies - ASC 606 - Impact - Balance sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Oct. 01, 2018	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	$ 35,056	$ 32,091	$ 31,741
Other assets	23,250	6,777	5,294
Deferred revenue	31,200	28,734	25,884
Accumulated deficit	(991,525)	(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	31,141
Other assets	22,163
Deferred revenue	28,328
Accumulated deficit	(993,655)
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	3,915
Other assets	1,087
Deferred revenue	2,872
Accumulated deficit	$ 2,130