Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (15,871)	$ (9,632)	$ (47,371)	$ (25,956)
Other comprehensive income (loss);
Unrealized gain (loss) on fair value of investments	(41)	6	48	27
Unrealized gain (loss) on currency translation	(2)	10	(1)	(14)
Comprehensive loss	$ (15,914)	$ (9,616)	$ (47,324)	$ (25,943)