CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (23,852)	$ (10,217)
Other comprehensive gain (loss):
Change in unrealized gain (loss) on available for sale securities, net	83	(13)
Total other comprehensive gain (loss)	83	(13)
Comprehensive loss	$ (23,769)	$ (10,230)