Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (77,400)	$ (43,562)	$ (47,089)
Other comprehensive income (loss):
Change in unrealized gain (loss) on short-term investments	59	(42)	(28)
Comprehensive loss	$ (77,341)	$ (43,604)	$ (47,117)