Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Consolidated Statements of Comprehensive Loss (Unaudited) [Abstract]
Net loss	$ (19,284)	$ (16,089)	$ (57,415)	$ (47,199)
Other comprehensive loss
Net unrealized gain (loss) on investments	(27)	(128)	244	(207)
Total comprehensive loss	$ (19,311)	$ (16,217)	$ (57,171)	$ (47,406)