Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (35,252)	$ (13,932)	$ (31,895)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(1,940)	54	9
Unrealized gain (loss) on available-for-sale marketable securities, net of reclassification adjustments for realized amounts	146	51	(15)
Employee retirement benefits	(578)	0	0
Other comprehensive income (loss), net of tax	(2,372)	105	(6)
Comprehensive loss, net of tax	$ (37,624)	$ (13,827)	$ (31,901)