Retirement Plans (Amount Recongized in the Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 27, 2014	Dec. 28, 2013
Pensions [Member]
Liabilities [Abstract]
Other current liabilities	$ 0	$ 0
Other liabilities	97,691	58,234
Total liabilities	97,691	58,234
Supplemental Employee Retirement Plans [Member]
Liabilities [Abstract]
Other current liabilities	1,989	2,077
Other liabilities	16,519	15,747
Total liabilities	18,508	17,824
Other Postretirement Benefit Plans [Member]
Liabilities [Abstract]
Other current liabilities	164	250
Other liabilities	1,625	1,825
Total liabilities	$ 1,789	$ 2,075