Investments: (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 28, 2014	Jun. 27, 2015	Jun. 28, 2014	Dec. 27, 2014
Summary of marketable securities classified as available-for-sale securities
Equity securities, Cost		$ 238,600		$ 526,600
Equity securities, Fair Value		215,200		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		(23,400)		(63,100)
Net unrealized losses		(23,400)		$ (59,800)
Realized gains and losses recognized on sales of available-for-sale marketable securities
Realized gains	$ 4,600	13,400	$ 26,800
Realized losses	(13,500)	(36,200)	(26,300)
Net realized gains (losses)	$ (8,900)	$ (22,800)	$ 500