Shareholders' Equity: (Details 2) (USD $)	9 Months Ended			12 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 27, 2014 Stock options	Dec. 28, 2013 Stock options	Sep. 27, 2014 2001 Plan Stock options	Sep. 27, 2014 2010 Plan Stock options	Apr. 30, 2014 2010 Plan Stock options	Sep. 27, 2014 Nonemployee Directors Plan Stock options	Apr. 30, 2014 Nonemployee Directors Plan Stock options
Stock option plans
Number of shares authorized for issuance					750,000	500,000	250,000	350,000	300,000
Number of Shares
Outstanding at the beginning of the period (in shares)			526,712
Granted (in shares)			48,500
Exercised (in shares)			(20,012)
Forfeited (in shares)			(5,000)
Outstanding at the end of the period (in shares)			550,200	526,712
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)			$ 42.87
Granted (in dollars per share)			$ 66.29
Exercised (in dollars per share)			$ 19.59
Forfeited (in dollars per share)			$ 56.85
Outstanding at the end of the period (in dollars per share)			$ 45.65	$ 42.87
Exercisable at the end of the period (in dollars per share)			$ 33.17
Exercisable at the end of the period (in shares)			305,748
Weighted Average Remaining Contractual Life (years)
Outstanding			6 years 10 months 28 days	7 years 3 months 29 days
Exercisable at the end of the period			5 years 9 months 4 days
Intrinsic Value
Outstanding at the beginning of the period			$ 26,446,700
Outstanding at the end of the period			16,500,100	26,446,700
Exercisable at the end of the period			$ 12,781,100
Weighted average assumptions and results used in estimation of fair value of options granted
Risk free interest rate (as a percent)	1.80%	1.30%
Expected life (years)	6 years	6 years
Expected volatility (as a percent)	34.10%	32.50%
Dividend yield (as a percent)	1.80%	1.90%
Option fair value (in dollars per share)	$ 19.23	$ 15.84