Adoption of Accounting Standards Codification 606 - Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	$ 1,591	$ 3,823	$ 4,191	$ 5,938
Other Comprehensive Income (Loss), Net of Tax:
Amortization of actuarial losses and prior service costs, net of tax benefit of $44 and $88 for the three months ended June 30, 2018 and July 1, 2017, respectively, and $89 and $151 for the six months ended June 30, 2018 and July 1, 2017, respectively	142	114	283	254
Change in unrealized gains and losses on cash flow hedges, net of tax of $28 and $72 for the three months ended June 30, 2018 and July 1, 2017, respectively, and $89 and $144 for the six months ended June 30, 2018 and July 1, 2017, respectively	87	(122)	281	(243)
Other Comprehensive Income (Loss), Net of Tax	229	(8)	564	11
Comprehensive Income	1,820	3,815	4,755	5,949
Amortization of actuarial losses and prior service costs, tax benefits	44	88	89	151
Change in unrealized gains and losses on cash flow hedges, tax benefit	28	$ 72	89	$ 144
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	(2,541)		(4,259)
Other Comprehensive Income (Loss), Net of Tax:
Amortization of actuarial losses and prior service costs, net of tax benefit of $44 and $88 for the three months ended June 30, 2018 and July 1, 2017, respectively, and $89 and $151 for the six months ended June 30, 2018 and July 1, 2017, respectively	0		0
Change in unrealized gains and losses on cash flow hedges, net of tax of $28 and $72 for the three months ended June 30, 2018 and July 1, 2017, respectively, and $89 and $144 for the six months ended June 30, 2018 and July 1, 2017, respectively	0		0
Other Comprehensive Income (Loss), Net of Tax	0		0
Comprehensive Income	(2,541)		(4,259)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	(950)		(68)
Other Comprehensive Income (Loss), Net of Tax:
Amortization of actuarial losses and prior service costs, net of tax benefit of $44 and $88 for the three months ended June 30, 2018 and July 1, 2017, respectively, and $89 and $151 for the six months ended June 30, 2018 and July 1, 2017, respectively	142		283
Change in unrealized gains and losses on cash flow hedges, net of tax of $28 and $72 for the three months ended June 30, 2018 and July 1, 2017, respectively, and $89 and $144 for the six months ended June 30, 2018 and July 1, 2017, respectively	87		281
Other Comprehensive Income (Loss), Net of Tax	229		564
Comprehensive Income	$ (721)		$ 496