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	$ (31,498)	$ (63,591)	$ (41,634)	$ (155,264)
Unrealized gains on debt securities, net of tax	64	37	286	143
Currency translation adjustment	(17)	(29)	(25)	19
Comprehensive loss	$ (31,451)	$ (63,583)	$ (41,373)	$ (155,102)