Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (16,640)	$ (12,491)	$ (36,827)	$ (29,123)
Change in unrealized gain (loss) on available-for-sale securities	230	(51)	131	(163)
Comprehensive loss	$ (16,410)	$ (12,542)	$ (36,696)	$ (29,286)

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

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