Shareholders' Equity: (Details 3) (USD $)	12 Months Ended
	Dec. 29, 2012	Dec. 31, 2011
$12.75 - $18.40
Additional disclosures
Shares of previously owned common stock surrendered as payment for option shares exercised	31,351	2,208
Stock options
Options Outstanding
Number Outstanding (in shares)	613,727
Weighted Average Remaining Contractual Life	7 years 22 days
Weighted Average Exercise Price (in dollars per share)	31.46
Options Exercisable
Number Exercisable (in shares)	351,463
Weighted Average Exercise Price (in dollars per share)	21.79
Additional disclosures
Total intrinsic value of options exercised	7,400,000	1,800,000
Total fair value of shares vested	2,800,000	2,200,000
Compensation expense	930,200	755,700
Total unrecognized compensation expense	2,700,000
Weighted average period for recognition of unrecognized compensation expense	2 years 8 months 12 days
Stock options | $12.75 - $18.40
Stock options outstanding and exercisable
Range of Exercise Price, low end of range (in dollars per share)	12.75
Range of Exercise Price, high end of range (in dollars per share)	18.40
Options Outstanding
Number Outstanding (in shares)	136,726
Weighted Average Remaining Contractual Life	5 years 11 months 19 days
Weighted Average Exercise Price (in dollars per share)	14.05
Options Exercisable
Number Exercisable (in shares)	124,348
Weighted Average Exercise Price (in dollars per share)	14.15
Stock options | $20.32 - $31.19
Stock options outstanding and exercisable
Range of Exercise Price, low end of range (in dollars per share)	20.32
Range of Exercise Price, high end of range (in dollars per share)	31.19
Options Outstanding
Number Outstanding (in shares)	219,001
Weighted Average Remaining Contractual Life	5 years 5 months 16 days
Weighted Average Exercise Price (in dollars per share)	23.60
Options Exercisable
Number Exercisable (in shares)	182,123
Weighted Average Exercise Price (in dollars per share)	22.69
Stock options | $32.92 - $51.17
Stock options outstanding and exercisable
Range of Exercise Price, low end of range (in dollars per share)	32.92
Range of Exercise Price, high end of range (in dollars per share)	51.17
Options Outstanding
Number Outstanding (in shares)	139,250
Weighted Average Remaining Contractual Life	8 years 7 months 2 days
Weighted Average Exercise Price (in dollars per share)	40.74
Options Exercisable
Number Exercisable (in shares)	33,621
Weighted Average Exercise Price (in dollars per share)	34.52
Stock options | $53.34 - $57.34
Stock options outstanding and exercisable
Range of Exercise Price, low end of range (in dollars per share)	53.34
Range of Exercise Price, high end of range (in dollars per share)	57.34
Options Outstanding
Number Outstanding (in shares)	118,750
Weighted Average Remaining Contractual Life	9 years 5 months 16 days
Weighted Average Exercise Price (in dollars per share)	55.13
Options Exercisable
Number Exercisable (in shares)	11,371
Weighted Average Exercise Price (in dollars per share)	53.34