GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Newmark
Non-amortized intangible assets
Carrying value of trade names	$ 11,111	$ 11,111
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	8,283	9,973
Webforge
Non-amortized intangible assets
Carrying value of trade names	9,105	9,432
Convert Italia S.p.A
Non-amortized intangible assets
Carrying value of trade names	8,703	0
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,424	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	21,128	22,647
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 69,754	$ 64,853