Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (20,952)	$ (23,146)	$ (62,957)	$ (69,037)
Other comprehensive income (loss):
Unrealized (loss) gain on marketable securities, net of tax of $0	(7)	111	324	16
Foreign currency translation adjustments, net of tax of $0	(1,213)	(24)	(1,442)	(642)
Comprehensive loss	$ (22,172)	$ (23,059)	$ (64,075)	$ (69,663)