Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (11,984)	$ (11,424)
Other comprehensive income:
Unrealized gain on available for sale securities	40	4
Comprehensive loss	$ (11,944)	$ (11,420)

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

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