Investments: (Details) (USD $)	12 Months Ended
	Dec. 27, 2014	Dec. 28, 2013	Dec. 29, 2012
Summary of marketable securities classified as available-for-sale securities
Equity securities, Cost	$ 526,600	$ 743,100
Equity securities, Fair Value	466,800	736,500
Unrealized gains and losses for marketable securities classified as available-for-sale securities in accumulated other comprehensive loss
Unrealized gains	3,300	6,800
Unrealized losses	(63,100)	(13,400)	(6,500)
Net unrealized losses	(59,800)	(6,600)	(6,500)
Realized gains and losses recognized on sales of available-for-sale marketable securities
Realized gains	40,900	25,200	52,500
Realized losses	(32,200)		(31,300)
Net realized gains/(losses)	$ 8,700	$ 25,200	$ 21,200