GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Mar. 28, 2020	Dec. 28, 2019
Newmark
Non-amortized intangible assets
Carrying value of trade names	$ 11,111	$ 11,111
Webforge
Non-amortized intangible assets
Carrying value of trade names	8,704	9,143
Convert Italia S.p.A
Non-amortized intangible assets
Carrying value of trade names	8,352	8,378
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	7,929	7,966
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,096	7,454
Walpar
Non-amortized intangible assets
Carrying value of trade names	3,500	3,500
Shakespeare
Non-amortized intangible assets
Carrying value of trade names	4,000	4,000
Other
Non-amortized intangible assets
Carrying value of trade names	16,852	17,555
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 67,544	$ 69,107