Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (40,696)	$ (77,400)	$ (43,562)
Other comprehensive income (loss):
Change in unrealized gain (loss) on short-term investments	185	59	(42)
Comprehensive loss	$ (40,511)	$ (77,341)	$ (43,604)