Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Financial Position [Abstract]
Net loss	$ (15,659)	$ (12,493)	$ (34,045)	$ (24,884)
Change in unrealized gain (loss) on investments	290	43	489	(74)
Comprehensive loss	$ (15,369)	$ (12,450)	$ (33,556)	$ (24,958)

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

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