GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 30, 2017
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	$ 9,717	$ 9,973
Webforge
Non-amortized intangible assets
Carrying value of trade names	9,230	9,432
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,526	7,690
Shakespeare
Non-amortized intangible assets
Carrying value of trade names	4,000	4,000
Other
Non-amortized intangible assets
Carrying value of trade names	$ 16,894	$ 22,647