Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017
Income Taxes [Abstract]
Accounts receivable	$ 588	$ 542
Compensated absences	355	848
Employment incentives	842	388
Employee benefit plans	4,914	5,581
General liability insurance	2,702	2,991
Postretirement benefit obligations	5,272	5,365
Net operating loss carryforwards	8,030	7,745
Other	7,967	4,373
Total deferred tax assets	30,670	27,833
Inventories	(9,828)	(8,026)
Unrealized gains on marketable securities	(1,809)	(2,310)
Nondeductible accruals and other	(5,274)	(5,160)
Depreciation	(104,552)	(99,759)
Total deferred tax liabilities	(121,463)	(115,255)
Net deferred tax liability	$ (90,793)	$ (87,422)