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	$ (55,545)	$ (45,470)	$ (49,000)
Other comprehensive loss:
Change in fair value of investments	8	(23)	(19)
Adjustment for net losses realized and included in net loss	0	3	0
Total change in unrealized losses on investments	8	(20)	(19)
Comprehensive loss	$ (55,537)	$ (45,490)	$ (49,019)