Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 28, 2019	Dec. 29, 2018
Income Taxes [Abstract]
Accounts receivable	$ 749	$ 588
Compensated absences	0	355
Employment incentives	1,405	842
Employee benefit plans	4,853	4,914
General liability insurance	2,778	2,702
Postretirement benefit obligations	5,767	5,272
Net operating loss carryforwards	6,582	8,030
Other	8,136	7,967
Total deferred tax assets	30,270	30,670
Inventories	(13,072)	(9,828)
Unrealized gains on marketable securities	(2,851)	(1,809)
Nondeductible accruals and other	(5,252)	(5,274)
Depreciation	(106,136)	(104,552)
Total deferred tax liabilities	(127,311)	(121,463)
Net deferred tax liability	$ (97,041)	$ (90,793)