Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
Income Taxes [Abstract]
Accounts receivable	$ 586	$ 813
Compensated absences	1,076	983
Employment incentives	9,826	3,143
Employee benefit plans	9,243	10,485
General liability insurance	4,359	4,048
Postretirement benefit obligations	6,484	5,906
Net operating loss carryforwards	5,600	5,926
Other	2,224	2,173
Total deferred tax assets	39,398	33,477
Inventories	(7,619)	(6,808)
Unrealized gains on marketable securities	(3,382)	(3,323)
Nondeductible accruals and other	(7,517)	(9,240)
Depreciation	(140,325)	(111,126)
Total deferred tax liabilities	(158,843)	(130,497)
Net deferred tax liability	$ (119,445)	$ (97,020)