INCOME TAXES. (Details 2) (USD $)	12 Months Ended
	Dec. 28, 2013	Dec. 29, 2012	Dec. 31, 2011
Reconciliation of the tax provision for income taxes (as a percent)
Statutory federal income tax rate (as a percent)	34.00%	35.00%	34.00%
State income taxes, net of federal benefit (as a percent)	1.20%	2.90%	(16.10%)
Tax-exempt underwriting income of wholly-owned small captive insurance subsidiary (as a percent)	(2.40%)
Domestic production deduction (as a percent)	(1.80%)	(2.60%)
Research and development tax credits (as a percent)	(1.10%)		(11.70%)
Alternative fuel tax credit (as a percent)	(0.40%)		(6.90%)
Stock-based compensation (as a percent)	0.10%	0.30%	(2.80%)
Change in valuation allowance (as a percent)		(39.80%)	(28.40%)
Other, net (as a percent)	1.20%	1.50%	0.20%
Effective tax rate (as a percent)	30.80%	(2.70%)	(31.70%)
Reconciliation of the change in the unrecognized tax benefits
Unrecognized tax benefits at the beginning of the period	$ 519,611	$ 719,612	$ 1,040,054
Gross increases - tax positions in prior periods	197,310	22,430	80,558
Lapse of statute of limitations	(57,921)	(222,431)	(401,000)
Unrecognized tax benefits at the end of the period	659,000	519,611	719,612
Unrecognized tax benefits, if recognized, would effect annual effective tax rate	$ 659,000