Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (12,682)	$ (12,407)	$ (27,070)	$ (25,009)
Other comprehensive income (loss):
Unrealized gain (loss) on cash equivalents	5	6	2	7
Total comprehensive loss	$ (12,677)	$ (12,401)	$ (27,068)	$ (25,002)