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Investments: (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 25, 2016
Jun. 25, 2016
Jul. 01, 2017
Dec. 31, 2016
Summary of marketable securities classified as available-for-sale securities        
Equity securities, Cost     $ 215,800 $ 215,800
Equity securities, Fair Value     216,500 199,900
Unrealized gains and losses for marketable securities classified as available-for-sale securities in accumulated other comprehensive loss        
Unrealized gains     9,400  
Unrealized losses     (8,700) (15,900)
Net unrealized losses     $ 700 $ (15,900)
Realized gains and losses recognized on sales of available-for-sale marketable securities        
Realized losses $ (6,400) $ (12,600)    
Net realized losses $ (6,400) $ (12,600)