Investments: (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 27, 2014	Sep. 26, 2015	Sep. 27, 2014	Dec. 27, 2014
Summary of marketable securities classified as available-for-sale securities
Equity securities, Cost		$ 280,600		$ 526,600
Equity securities, Fair Value		226,500		466,800
Unrealized gains and losses for marketable securities classified as available-for-sale securities in accumulated other comprehensive loss
Unrealized gains				3,300
Unrealized losses		(54,100)		(63,100)
Net unrealized losses		(54,100)		$ (59,800)
Realized gains and losses recognized on sales of available-for-sale marketable securities
Realized gains	$ 12,200	13,400	$ 39,000
Realized losses		(36,200)	(26,300)
Net realized gains (losses)	$ 12,200	$ (22,800)	$ 12,700