CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (37,323)	$ (62,046)	$ (10,136)	$ (91,673)
Unrealized gains on debt securities, net of tax	10	151	222	106
Currency translation adjustment	(93)	20	(8)	48
Comprehensive loss	$ (37,406)	$ (61,875)	$ (9,922)	$ (91,519)

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

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