Commitments and Contingencies: (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Employee Benefit Plan
Service period for vesting of employer contribution	5 years
Company contributions	$ 309,800	$ 324,600	$ 297,400
Operating Leases
Rent expense under operating leases	1,066,500	1,063,900	$ 1,026,800
Minimum rental commitments
2017	705,000
2018	718,800
2019	451,100
Total	1,874,900
Total deferred rent	600,000	800,000
Deferred rent included in other liabilities	$ 400,000	$ 600,000