Accumulated Other Comprehensive Items - Reclassification Out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Other expense, net	$ (245)	$ (217)	$ (491)	$ (421)
Interest expense	(1,850)	(392)	(3,582)	(740)
Cost of revenues	(86,749)	(57,390)	(169,863)	(111,230)
Amortization of Actuarial Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Total Reclassifications			(278)
Amortization of Prior Service Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Total Reclassifications			(36)
Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Total Reclassifications			1
Reclassification out of Accumulated Other Comprehensive Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Total Reclassifications	(152)	(120)	(313)	(246)
Reclassification out of Accumulated Other Comprehensive Items [Member] | Pension and Other Post-retirement Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Total income (expense) before income taxes	(208)	(181)	(417)	(351)
Provision for income taxes	51	64	103	123
Total Reclassifications	(157)	(117)	(314)	(228)
Reclassification out of Accumulated Other Comprehensive Items [Member] | Amortization of Actuarial Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Other expense, net	(184)	(144)	(369)	(279)
Reclassification out of Accumulated Other Comprehensive Items [Member] | Amortization of Prior Service Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Other expense, net	(24)	(37)	(48)	(72)
Reclassification out of Accumulated Other Comprehensive Items [Member] | Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Total income (expense) before income taxes	7	(6)	2	(29)
Provision for income taxes	(2)	3	(1)	11
Total Reclassifications	5	(3)	1	(18)
Reclassification out of Accumulated Other Comprehensive Items [Member] | Cash Flow Hedges [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Interest expense	(17)	(6)	(22)	(18)
Reclassification out of Accumulated Other Comprehensive Items [Member] | Cash Flow Hedges [Member] | Forward Currency-Exchange Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Items [Line Items]
Cost of revenues	$ 24	$ 0	$ 24	$ (11)