Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (11,531)	$ (3,277)	$ (35,607)	$ (21,798)
Unrealized gain on short-term investments	0	41	363	370
Currency translation adjustments	(4,718)	0	(4,091)	0
Changes in pension plan assets and benefit obligations	0	(24)	(1)	(2)
Tax effect of the above-listed adjustments	0	(8)	(85)	(134)
Total comprehensive loss	$ (16,249)	$ (3,268)	$ (39,421)	$ (21,564)