Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 26, 2020	Dec. 28, 2019
Income Taxes [Abstract]
Accounts receivable	$ 659	$ 749
Employment incentives	6,204	4,735
Self-insurance liability	8,515	7,344
Postretirement benefit obligations	6,527	6,054
Net operating loss and credit carryforwards	7,787	9,945
Unrecognized Tax Benefits	1,751	1,389
Other	1,407	611
Total deferred tax assets	32,850	30,827
Inventories	(13,407)	(13,072)
Unrealized gains on marketable securities	(3,059)	(2,851)
Prepaids	(5,993)	(4,883)
Nondeductible accruals and other	(332)	(926)
Depreciation	(113,463)	(106,136)
Total deferred tax liabilities	(136,254)	(127,868)
Net deferred tax liability	$ (103,404)	$ (97,041)