Retirement Plans (Amounts Recognized in Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 27, 2014	Dec. 28, 2013
Pensions [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]
Net actuarial loss (gain)	$ 115,438	$ 60,338
Prior service cost	0	0
Total	115,438	60,338
Supplemental Employee Retirement Plans [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]
Net actuarial loss (gain)	5,872	4,158
Prior service cost	0	0
Total	5,872	4,158
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]
Net actuarial loss (gain)	(830)	(614)
Prior service cost	44	44
Total	$ (786)	$ (570)