Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Significant Accounting Policies [Line Items]
Fiscal Period Duration	364 days	364 days	364 days
Unrealized gain (loss) on equity securities	$ (1,791)	$ 1,975	$ (1,606)
Accounts Receivable, Allowance for Credit Loss	$ 2,400	2,800
Percentage of facilities under operating lease	51.00%
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 444
Finite-Lived Intangible Assets, Amortization Expense, Year Two	320
Finite-Lived Intangible Assets, Amortization Expense, Year Three	310
Finite-Lived Intangible Assets, Amortization Expense, Year Four	310
Finite-Lived Intangible Assets, Amortization Expense, Year Five	147
Impairment of Long-Lived Assets Held-for-use	0	0	1,532
Self Insurance, Annual Maximum of Health Claims Liability per Associate	500
Stop loss insurance aggregating deductible	450
Cost of Goods Sold, Vendor Allowances	133,500	130,400	132,000
Vendor Paid Cooperative Advertising Credits	21,700	24,800	19,400
Accounts Receivable, Earned Advertising Credits	886,000	1,000
Accounts Receivable, Earned Promotional Discounts	8,600	9,500
Unearned Income for Vendor Programs	3,300	5,400
Advertising Expense	24,500	30,300	30,500
Commission income	17,700	18,300	$ 17,900
Investments [Member]
Significant Accounting Policies [Line Items]
Cash Equivalents, at Carrying Value	95,900	32,900
Consumer Electronic Payments [Member]
Significant Accounting Policies [Line Items]
Cash Equivalents, at Carrying Value	$ 41,700	$ 23,100
Maximum [Member]
Significant Accounting Policies [Line Items]
Lease renewal term	20 years
Self Insurance, Maximum of Workers Compensation Claims Liability per Associate per Claim	$ 2,000
Property and Casualty Insurance, Deductible	$ 1,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Lease renewal term	5 years
Self Insurance, Maximum of Workers Compensation Claims Liability per Associate per Claim	$ 1,000
Property and Casualty Insurance, Deductible	$ 100
Customer Lists [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years