Receivables: (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Current receivables
Trade	$ 12,200	$ 7,600
Royalty	1,302,700	1,242,800
Other	164,300	166,500
Total current receivables	1,479,200	1,416,900
Activity in the allowance for doubtful accounts for trade receivables
Balance at beginning of year	200	1,600	$ 4,300
Provisions charged to expense	2,800	1,500	(200)
Deductions for amounts written-off	(900)	(2,900)	(2,500)
Balance at end of year	$ 2,100	$ 200	$ 1,600