Shareholders' Equity (Deficit): (Details 2) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 26, 2015	Sep. 27, 2014	Dec. 27, 2014
Weighted Average Remaining Contractual Life (years)
Outstanding	6 years 4 months 28 days		6 years 11 months 5 days
Exercisable at the end of the period	5 years 3 months 11 days
Stock options
Number of Shares
Outstanding at the beginning of the period (in shares)	597,700
Granted (in shares)	39,700
Exercised (in shares)	(5,106)
Outstanding at the end of the period (in shares)	632,294		597,700
Exercisable at the end of the period (in shares)	397,392
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 48.50
Granted (in dollars per share)	91.93
Exercised (in dollars per share)	40.52
Outstanding at the end of the period (in dollars per share)	51.29		$ 48.50
Exercisable at the end of the period (in dollars per share)	$ 38.58
Intrinsic Value
Outstanding at the beginning of the period	$ 20,973,700
Outstanding at the end of the period	30,798,700		$ 20,973,700
Exercisable at the end of the period	$ 24,405,900
Weighted average assumptions and results used in estimation of fair value of options granted
Risk free interest rate (as a percent)	1.68%	1.80%
Expected life (years)	6 years	6 years
Expected volatility (as a percent)	30.80%	34.10%
Dividend yield (as a percent)	1.34%	1.80%
Option fair value (in dollars per share)	$ 25.48	$ 19.23
2001 Plan | Stock options
Stock option plans
Number of shares authorized for issuance	750,000
2010 Plan | Stock options
Stock option plans
Number of shares authorized for issuance	500,000
Nonemployee Directors Plan | Stock options
Stock option plans
Number of shares authorized for issuance	350,000