Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Accounts receivable	$ 542	$ 586
Compensated absences	848	1,076
Employment incentives	388	9,826
Employee benefit plans	5,581	9,243
General liability insurance	2,991	4,359
Postretirement benefit obligations	5,365	6,484
Net operating loss carryforwards	7,745	5,600
Other	4,373	2,224
Total deferred tax assets	27,833	39,398
Inventories	(8,026)	(7,619)
Unrealized gains on marketable securities	(2,310)	(3,382)
Nondeductible accruals and other	(5,160)	(7,517)
Depreciation	(99,759)	(140,325)
Total deferred tax liabilities	(115,255)	(158,843)
Net deferred tax liability	$ (87,422)	$ (119,445)