Summary of Significant Accounting Policies - ASC 606 - Impact - Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Oct. 01, 2018	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other current assets	$ 40,441	$ 32,091	$ 31,741
Other assets	21,126	6,777	5,294
Deferred revenue	30,598	28,734	25,884
Accumulated deficit	(991,499)	(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	36,388
Other assets	20,212
Deferred revenue	28,033
Accumulated deficit	(993,901)
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	4,053
Other assets	914
Deferred revenue	2,565
Accumulated deficit	$ 2,402