Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss	$ (13,694)	$ (17,710)	$ (21,283)
Other comprehensive income (loss):
Unrealized losses on short-term investments	(27)
Unrealized gains (losses) on derivative instruments	642	(148)	(5)
Total other comprehensive income (loss)	615	(148)	(5)
Comprehensive loss	$ (13,079)	$ (17,858)	$ (21,288)