Post-Retirement Health Care (Schedule of Cost of Retirement Plans) (Details) - Postretirement Health Coverage - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 30, 2017	Dec. 31, 2016
Change in benefit obligation
Benefit obligation at beginning of year	$ 21,153	$ 20,884
Service cost	741	735
Interest cost	825	846
Benefits paid	(1,003)	(1,017)
Actuarial (gain) loss	1,217	(295)
Benefit obligation at end of year	22,933	21,153
Change in plan assets
Fair value at beginning of year	0	0
Actual return on assets	0	0
Employer contribution	1,003	1,017
Transferred out	0	0
Benefits paid	(1,003)	(1,017)
Fair value at end of year	0	0
Funded Status of Plan			$ (22,933)	$ (21,153)
Amounts recognized in the Statement of Financial Position consist of:
Current liabilities			1,050	1,034
Non-current liabilities			21,883	20,119
Amounts recognized in Accumulated Other Comprehensive Income (before tax) consist of:
Actuarial (gain) loss			3,565	2,373
Total Amount recognized in Accumulated Other Comprehensive Income (before tax)	2,373	2,730	$ 3,565	$ 2,373
Change in Accumulated Other Comprehensive Income (before tax):
Amount disclosed at beginning of year	2,373	2,730
Actuarial (gain) loss	1,217	(295)
Amortization of transition amount	(25)	(62)
Amount disclosed at end of year	$ 3,565	$ 2,373