GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Webforge
Non-amortized intangible assets
Carrying value of trade names	$ 9,793	$ 9,432
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	10,243	9,973
Newmark
Non-amortized intangible assets
Carrying value of trade names	11,111	11,111
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,985	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	17,495	22,647
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 60,627	$ 64,853