DISCLOSURES ABOUT THE FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($)	Dec. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets recorded for the investments held	$ 39,091,000	$ 35,784,000
Liabilities recorded for the investments held	37,963	36,439
Level 1 member
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	41,042,000	37,800,000
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	754,854,000	755,646,000
Trading Securities	41,042,000	37,800,000
Estimated fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	799,258,000	731,633,000
EMD
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of remaining ownership	1,951,000	2,016,000
Valmont Deferred Compensation Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets recorded for the investments held	$ 39,091,000	$ 35,784,000