Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (6,627)	$ (3,887)
Components of other comprehensive income/(loss), net of tax:
Foreign currency translation adjustments	(832)	322
Amortization of defined benefit pension items:
Net actuarial loss	134	147
Prior service cost	12	10
Defined benefit pension plan adjustments	146	157
Other comprehensive (loss)/income, net of tax	(686)	479
Comprehensive loss	$ (7,313)	$ (3,408)