Postretirement Benefits Amounts Recognized in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Jan. 01, 2017
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ 1,617	$ 1,972
Net gain	(2,928)	(3,272)
Deferred Tax Assets, Other Comprehensive Loss	326	499
Accumulated other comprehensive income	(1,210)	(1,203)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year	191
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year	(352)
Other Comprehensive Income (Loss) [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred Tax Assets, Other Comprehensive Loss	$ 101	$ 97