Shareholders' Equity: (Details) (USD $)	12 Months Ended
	Dec. 28, 2013	Dec. 29, 2012	Dec. 31, 2011
Dividends
Cash dividend approved by Board of Directors (in dollars per share)	$ 0.19	$ 0.15	$ 0.11
Aggregate quarterly cash dividends declared and paid	$ 960,000	$ 750,000	$ 550,000
Special cash dividend approved by Board of Directors (in dollars per share)		$ 5.00
Total special dividend in cash		25,400,000
Borrowings on line of credit for special dividend		12,800,000
Repurchase of Common Stock
Aggregate purchase price of shares repurchased (in dollars)	1,854,900	7,220,300	3,527,200
Common Stock Repurchase Program
Repurchase of Common Stock
Number of shares repurchased	28,422	134,720	99,494
Aggregate purchase price of shares repurchased (in dollars)	$ 1,900,000	$ 7,200,000	$ 3,500,000
Aggregate purchase price per share of shares repurchased (in dollars per share)	$ 65.26	$ 53.60	$ 35.45
Number of additional shares that can be repurchased	332,730