GOODWILL AND INTANGIBLE ASSETS - Impairment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2018	Sep. 29, 2018
Indefinite-lived Intangible Assets [Line Items]
Goodwill impairment loss	$ 14,355	$ 14,355
Valmont SM
Indefinite-lived Intangible Assets [Line Items]
Impairment indefinite-lived intangible assets	$ 1,425

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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