Summary Of Significant Accounting Policies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 28, 2019 USD ($) segment	Dec. 29, 2018 USD ($)	Dec. 30, 2017 USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments | segment	1
Fiscal Period Duration	364 days	364 days	364 days
Unrealized gain (loss) on equity securities	$ 1,975	$ (1,606)	$ 0
Accounts Receivable, Allowance for Credit Loss	$ 2,800	2,100
Percentage of facilities under operating lease	52.00%
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 455
Finite-Lived Intangible Assets, Amortization Expense, Year Two	444
Finite-Lived Intangible Assets, Amortization Expense, Year Three	314
Finite-Lived Intangible Assets, Amortization Expense, Year Four	310
Finite-Lived Intangible Assets, Amortization Expense, Year Five	310
Impairment of Long-Lived Assets Held-for-use	0	1,532	0
Self Insurance, Annual Maximum of Health Claims Liability per Associate	500
Self Insurance, Maximum of Workers Compensation Claims Liability per Associate per Claim	2,000
Stop loss insurance aggregating deductible	250
Cost of Goods Sold, Vendor Allowances	130,400	132,000	131,100
Vendor Paid Cooperative Advertising Credits	24,800	19,400	19,200
Accounts Receivable, Earned Advertising Credits	1,000	1,600
Accounts Receivable, Earned Promotional Discounts	9,500	12,800
Unearned Income for Vendor Programs	5,400	7,400
Advertising Expense	30,300	30,500	$ 31,000
Operating lease right-to-use	210,196	0
Operating lease liability	218,768
Investments [Member]
Significant Accounting Policies [Line Items]
Cash Equivalents, at Carrying Value	32,900	5,400
Consumer Electronic Payments [Member]
Significant Accounting Policies [Line Items]
Cash Equivalents, at Carrying Value	$ 23,100	23,600
Accounting Standards Update 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease right-to-use		202,000
Operating lease liability		$ 211,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Lease renewal term	20 years
Property and Casualty Insurance, Deductible	$ 1,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Lease renewal term	5 years
Property and Casualty Insurance, Deductible	$ 100
Customer Lists [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years