GOODWILL AND INTANGIBLE ASSETS (Details 2) - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017
Newmark
Non-amortized intangible assets
Carrying value of trade names	$ 11,111	$ 11,111
Webforge
Non-amortized intangible assets
Carrying value of trade names	8,872	9,432
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	8,155	9,973
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,233	7,690
Donhad
Non-amortized intangible assets
Carrying value of trade names	0	5,801
Shakespeare
Non-amortized intangible assets
Carrying value of trade names	4,000	4,000
Walpar, LLC [Member]
Non-amortized intangible assets
Carrying value of trade names	4,300	0
Convert
Non-amortized intangible assets
Carrying value of trade names	8,580	0
Other
Non-amortized intangible assets
Carrying value of trade names	16,472	16,846
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 68,723	$ 64,853