Income Taxes: (Details) (USD $)	12 Months Ended
	Jan. 03, 2012	Dec. 28, 2010	Dec. 29, 2009
Income Taxes:
Income before income taxes	$ 129,143,000	$ 111,089,000	$ 51,307,000
Current:
Federal	17,093,000	26,580,000	9,927,000
State	8,423,000	6,883,000	3,345,000
Total current	25,516,000	33,463,000	13,272,000
Deferred:
Federal	9,284,000	(4,024,000)	(4,318,000)
State	(1,377,000)	(63,000)	(480,000)
Total deferred	7,907,000	(4,087,000)	(4,798,000)
Total provision	33,423,000	29,376,000	8,474,000
Income Taxes Rate Reconciliation
Tax at U.S. federal statutory rate (as a percent)	35.00%	35.00%	35.00%
State and district income taxes, net of federal income tax benefit (as a percent)	3.60%	4.10%	3.70%
Tax credits and incentives (as a percent)	(9.10%)	(8.20%)	(17.00%)
Change in uncertain tax positions (as a percent)	(1.30%)	(0.70%)	(0.20%)
Manufacturing deduction (as a percent)	(2.70%)	(3.10%)	(2.60%)
Deferred compensation (as a percent)	0.20%	(0.60%)	(2.00%)
Other (as a percent)	0.20%	(0.10%)	(0.40%)
Effective tax rate (as a percent)	25.90%	26.40%	16.50%
Current deferred tax assets/(liabilities)
Employee benefits	7,638,000	8,025,000
Insurance	13,099,000	13,088,000
Prepaid expenses	(7,314,000)	(7,060,000)
Other, net	1,151,000	589,000
Current deferred tax assets/(liabilities)	14,574,000	14,642,000
Noncurrent deferred tax assets/(liabilities)
Property and equipment	(162,146,000)	(150,710,000)
Accrued rent	21,257,000	20,469,000
Stock-based compensation	20,800,000	19,230,000
Employee benefits	8,289,000	7,817,000
Tax credit carryforwards	1,918,000	2,015,000
Deferred income	5,690,000	5,762,000
Other, net	265,000	(411,000)
Noncurrent deferred tax assets/(liabilities)	(103,927,000)	(95,828,000)
Reconciliation of beginning and ending amount of unrecognized tax benefits
Balance at beginning of year	2,135,000	6,460,000	3,694,000
Additions based on tax positions taken during a prior period			139,000
Reductions based on tax positions taken during a prior period		(3,085,000)
Additions based on tax positions taken during the current period	199,000	163,000	3,334,000
Reductions related to settlements with taxing authorities and lapses of statutes of limitations	(1,744,000)	(1,403,000)	(707,000)
Balance at end of year	590,000	2,135,000	6,460,000
Unrecognized tax benefits, if recognized, would unfavorably affect the annual effective income tax rate	600,000
Recognized amount of accrued interest associated with uncertain tax positions	100,000	100,000	200,000
Recognized amount of accrued penalties associated with uncertain tax positions		200,000
Reversal of interest associated with settlements of disputes with taxing authorities and lapses of statutes of limitations	900,000	300,000	100,000
Accrued interest related with uncertain tax positions	100,000	800,000
Decrease in unrecognized tax benefits during the next twelve months based on the lapses of statutes of limitations for certain jurisdictions	100,000
State
Tax credit carryforwards
Tax credit carryforwards	$ 3,000,000	$ 3,100,000