CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (20,223)	$ (13,022)	$ (26,175)	$ (20,297)
Other comprehensive loss:
Unrealized gain (loss) related to marketable securities, net of tax	9	(28)	2	(71)
Reclassification adjustment for losses (gains) related to marketable securities included in other (expense) income, net of tax	0	30	(1)	200
Translation adjustment, net of tax	(1,129)	676	(540)	950
Change in actuarial valuation of defined benefit pension	0	(47)	0	(47)
Comprehensive loss	$ (21,343)	$ (12,391)	$ (26,714)	$ (19,265)

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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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

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