GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 26, 2015
Webforge
Non-amortized intangible assets
Carrying value of trade names	$ 9,061	$ 10,430
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	9,333	8,919
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	7,387	8,504
Donhad
Non-amortized intangible assets
Carrying value of trade names	5,573	6,415
Shakespeare
Non-amortized intangible assets
Carrying value of trade names	4,000	4,000
Industrial Galvanizers
Non-amortized intangible assets
Carrying value of trade names	2,313	2,662
Other
Non-amortized intangible assets
Carrying value of trade names	14,089	13,889
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 62,867	$ 65,930