GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Webforge
Non-amortized intangible assets
Carrying value of trade names	$ 9,362	$ 8,624
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	9,839	8,765
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	7,633	7,032
Donhad
Non-amortized intangible assets
Carrying value of trade names	5,758	5,305
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	2,390	2,201
Other
Non-amortized intangible assets
Carrying value of trade names	14,448	13,747
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 64,541	$ 60,785