GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 29, 2018
Newmark
Non-amortized intangible assets
Carrying value of trade names	$ 11,111	$ 11,111
Webforge
Non-amortized intangible assets
Carrying value of trade names	8,587	8,872
Convert Italia S.p.A
Non-amortized intangible assets
Carrying value of trade names	8,203	8,580
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	7,799	8,155
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,001	7,233
Walpar
Non-amortized intangible assets
Carrying value of trade names	3,500	4,300
Shakespeare
Non-amortized intangible assets
Carrying value of trade names	4,000	4,000
Other
Non-amortized intangible assets
Carrying value of trade names	17,211	16,472
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 67,412	$ 68,723