Shareholders' Equity: (Details 2) (Stock options, USD $)	3 Months Ended	12 Months Ended
	Mar. 28, 2015	Dec. 27, 2014
Number of Shares
Outstanding at the beginning of the period (in shares)	597,700
Exercised (in shares)	(1,669)
Outstanding at the end of the period (in shares)	596,031	597,700
Exercisable at the end of the period (in shares)	348,453
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 48.50
Exercised (in dollars per share)	$ 28.77
Outstanding at the end of the period (in dollars per share)	$ 48.55	$ 48.50
Exercisable at the end of the period (in dollars per share)	$ 36.27
Weighted Average Remaining Contractual Life (years)
Outstanding	6 years 8 months 9 days	6 years 11 months 5 days
Exercisable at the end of the period	5 years 6 months 4 days
Intrinsic Value
Outstanding at the beginning of the period	$ 20,973,700
Outstanding at the end of the period	22,282,900	20,973,700
Exercisable at the end of the period	$ 17,307,400
2001 Plan
Stock option plans
Number of shares authorized for issuance	750,000
2010 Plan
Stock option plans
Number of shares authorized for issuance	500,000
Nonemployee Directors Plan
Stock option plans
Number of shares authorized for issuance	350,000