Basis of Presentation and Summary of Significant Accounting Policies - Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (36,233)	$ (30,223)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue	(11,970)	(5,411)
Cash, cash equivalents and restricted cash, beginning of period	224,857	136,056
Cash, cash equivalents and restricted cash, end of period	$ 347,113	117,564
As Originally Reported | Accounting Standards Update 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		(24,384)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue		(11,250)
Cash, cash equivalents and restricted cash, beginning of period		135,797
Cash, cash equivalents and restricted cash, end of period		117,305
Effect of Change | Accounting Standards Update 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		(5,839)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue		5,839
Cash, cash equivalents and restricted cash, beginning of period		259
Cash, cash equivalents and restricted cash, end of period		$ 259