Summary of Significant Accounting Policies - Revenue - Summary of Deferred Revenue Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue	$ 237,574		$ 241,590
Other Long-term Liabilities	116,757		$ 73,039
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]
Deferred revenue	9,510	$ 9,671
Other Long-term Liabilities	$ 7,590	$ 9,877