Receivables: (Details) - USD ($)	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Current receivables
Trade	$ 9,800	$ 12,200
Royalty	1,574,500	1,302,700
Other	211,700	164,300
Total current receivables	1,796,000	1,479,200
Activity in the allowance for doubtful accounts for trade receivables
Balance at beginning of year	2,100	200	$ 1,600
Provisions charged to expense	(1,600)	2,800	1,500
Deductions for amounts written-off	(100)	(900)	(2,900)
Balance at end of year	$ 400	$ 2,100	$ 200