Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (8,393)	$ (12,162)
Unrealized losses	$ (747)	$ 881	(1,579)	1,203
Amounts reclassified from accumulated other comprehensive income (loss)			396	506
Tax effect			(103)	(192)
Net of tax amount			(1,286)	1,517
Ending balance	(9,679)	(10,645)	(9,679)	(10,645)
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(3,305)	(5,500)
Unrealized losses			(1,579)	1,203
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Tax effect			0	0
Net of tax amount			(1,579)	1,203
Ending balance	(4,884)	(4,297)	(4,884)	(4,297)
Defined benefit pension plans [member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(5,088)	(6,662)
Unrealized losses			0	0
Amounts reclassified from accumulated other comprehensive income (loss)			396	506
Tax effect			(103)	(192)
Net of tax amount			293	314
Ending balance	$ (4,795)	$ (6,348)	$ (4,795)	$ (6,348)