NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended	12 Months Ended
	Oct. 01, 2016 USD ($)	Dec. 30, 2017 USD ($) item	Dec. 31, 2016 USD ($) item
RETIREMENT PLANS
Unfunded liabilities related to the Supplemental Profit Sharing Plan		$ 1,027,000	$ 854,000
RESERVE FOR SELF-INSURED AND INSURED LOSSES
Amount of claims and related insured losses		0	32,000
RECLAMATION
Reserve for reclamation activities		6,165,000	5,940,000
Current portion of reserve for reclamation		981,000	748,000
Changes in the aggregated product warranty liability
Beginning balance		118,000	121,000
Warranty related expenditures		(211,000)	(120,000)
Warranty expense accrued		225,000	117,000
Ending balance		$ 132,000	$ 118,000
Fiscal year end
Length of fiscal year		364 days	364 days
Pueblo Colorado gravel operations
IMPAIRMENT OF LONG-LIVED ASSETS
Write off of prepaid royalties	$ 632,000
Total sales | Customer risk
CONCENTRATIONS
Number of customers accounted for 10% or more of total sales | item		0	0
Accounts Receivable | Customer risk
CONCENTRATIONS
Number of customers accounted for 10% or more of account receivable | item			0
Heating and Cooling | Customer risk
CONCENTRATIONS
Number of customers accounted for 10% or more of account receivable | item		1
Heating and Cooling | Accounts Receivable | Customer risk
CONCENTRATIONS
Concentration risk (as a percent)		18.00%