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	$ (32,077)	$ (7,093)	$ (67,318)	$ (24,075)
Unrealized (loss) gain on short-term investments		(107)		363
Currency translation adjustments	(928)	160	(121)	627
Changes in pension plan assets and benefit obligations		7		(1)
Tax effect of the above-listed adjustments	25	100	33	(85)
Total comprehensive loss	$ (32,980)	$ (6,933)	$ (67,406)	$ (23,171)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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