Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (35,231)	$ (17,322)	$ (1,673)
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on investments	27	(26)	(10)
Total other comprehensive income (loss)	27	(26)	(10)
Comprehensive loss	$ (35,204)	$ (17,348)	$ (1,683)