STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (27,017)	$ (27,916)	$ (29,537)
Net unrealized gain (loss) on marketable securities	24	(154)	160
Comprehensive loss	$ (26,993)	$ (28,070)	$ (29,377)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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