Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (52,078)	$ (40,969)	$ (52,023)
Other comprehensive income (loss):
Unrealized gains (losses) on cash equivalents	(6)	4	0
Foreign currency translation	1	(1)	(9)
Total comprehensive loss	$ (52,083)	$ (40,966)	$ (52,032)