Summary of Significant Accounting Policies - Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue - current		$ 33,558	$ 45,000
Accumulated deficit	$ (202,553)	(134,855)
As Originally Reported | Accounting Standards Update 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue - current		22,500
Accumulated deficit		(123,797)
Effect of Change | Accounting Standards Update 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue - current		11,058
Accumulated deficit		$ (11,058)