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	$ (7,068)	$ (14,442)
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on investments	16	(20)
Total other comprehensive income (loss)	16	(20)
Comprehensive loss	$ (7,052)	$ (14,462)