Summary of Significant Accounting Policies - ASC 606 - Cumulative Effect - Balance Sheet - Continuing Operations (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Oct. 01, 2018	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets	$ 42,063	$ 32,091	$ 31,741
Other assets	22,304	6,777	5,294
Long-term deferred tax assets	23,287	44,201	43,798
Deferred revenue	31,091	28,734	25,884
Accumulated deficit	$ (987,725)	(994,933)	$ (994,074)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets		350
Other assets		1,483
Long-term deferred tax assets		403
Deferred revenue		2,850
Accumulated deficit		$ (859)