INCOME TAXES. - Deferred (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Federal:
Current	$ 8,620,430	$ 5,496,735	$ 2,242,641
Deferred	(172,449)	99,251	1,100,487
Federal income tax expense (benefit)	8,447,981	5,595,986	3,343,128
State:
Current	701,664	489,684	227,648
Deferred	257,186	233,705	429,879
State income tax expense (benefit)	958,850	723,389	657,527
Total	9,406,831	6,319,375	$ 4,000,655
Deferred tax assets:
Receivables	18,757	20,020
Inventories	575,675	612,830
Accrued liabilities	1,330,441	1,028,149
Net operating losses and credit carryforwards	2,263,667	1,906,406
Other	413,374	93,600
Gross deferred tax assets	4,601,914	3,661,005
Valuation allowance	(1,072,022)	(784,925)
Total deferred tax assets	3,529,892	2,876,080
Deferred tax liabilities:
Depreciation	(4,317,934)	(4,265,972)
Prepaids and other	(1,393,736)	(707,149)
Total deferred tax liabilities	(5,711,670)	(4,973,121)
Net deferred tax liabilities	(2,181,778)	(2,097,041)
State
Income Tax Disclosures
Tax loss carryforwards	23,100,000
Deferred tax liabilities:
Valuation allowance for deferred tax assets related to net operating loss carryforwards	200,000
Deferred tax assets, credit carry forwards	1,000,000	900,000
Valuation allowance for credits	$ 900,000	$ 800,000