NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended	12 Months Ended
	Oct. 01, 2016 USD ($)	Dec. 31, 2016 USD ($) item	Jan. 02, 2016 USD ($) item
RETIREMENT PLANS
Unfunded liabilities related to the Supplemental Profit Sharing Plan		$ 854,000	$ 901,000
RESERVE FOR SELF-INSURED AND INSURED LOSSES
Amount of claims and related insured losses		32,000	0
RECLAMATION
Reserve for reclamation activities		5,940,000	5,675,000
Current portion of reserve for reclamation		748,000	695,000
Changes in the aggregated product warranty liability
Beginning balance		121,000	109,000
Warranty related expenditures		(120,000)	(150,000)
Warranty expense accrued		117,000	162,000
Ending balance		$ 118,000	$ 121,000
CONCENTRATIONS
Number of customers accounted for 10% or more of total sales | item		0	0
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