INCOME TAXES. (Details 2) (USD $)	12 Months Ended
	Dec. 27, 2014	Dec. 28, 2013	Dec. 29, 2012
Reconciliation of the tax provision for income taxes (as a percent)
Statutory federal income tax rate (as a percent)	35.00%	34.00%	35.00%
State income taxes, net of federal benefit (as a percent)	5.00%	3.00%	3.10%
Tax-exempt underwriting income of wholly-owned small captive insurance subsidiary (as a percent)	(2.40%)	(1.30%)
Domestic production deduction (as a percent)	(2.30%)	(1.00%)	(2.40%)
Research and development tax credits (as a percent)	(0.60%)	(0.60%)
Alternative fuel tax credit (as a percent)	(0.20%)	(0.20%)
Stock-based compensation (as a percent)	(0.90%)	0.10%	0.20%
Change in valuation allowance (as a percent)			(36.80%)
Other, net (as a percent)	(1.50%)	0.60%	1.40%
Effective tax (as a percent)	32.10%	34.60%	0.50%
Reconciliation of the change in the unrecognized tax benefits
Unrecognized tax benefits at the beginning of the period	$ 659,000	$ 519,611	$ 719,612
Gross increases - tax positions in prior periods	157,657	197,310	22,430
Lapse of statute of limitations	(70,657)	(57,921)	(222,431)
Unrecognized tax benefits at the end of the period	746,000	659,000	519,611
Reconciliation of the provision for income taxes
U.S. Federal statutory tax rate	4,364,717	5,821,356	4,356,433
State income taxes, net of federal benefit	617,410	510,783	388,840
Tax-exempt underwriting income of wholly-owned small captive insurance subsidiary	(297,243)	(225,480)
Domestic production deduction	(281,688)	(167,800)	(304,300)
Research and development tax credits	(75,000)	(100,000)
Alternative fuel tax credit	(22,750)	(37,370)
Stock-based compensation	(117,395)	16,800	30,580
Valuation allowance			(4,589,180)
Other, net	(187,396)	105,070	182,262
Effective Tax Rate	$ 4,000,655	$ 5,923,359	$ 64,635