GOODWILL AND INTANGIBLE ASSETS - Carrying Values of Trade Names - (Details) - USD ($) $ in Thousands	Jun. 29, 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	8,872	8,872
Convert Italia S.p.A
Non-amortized intangible assets
Carrying value of trade names	8,526	8,580
Valmont SM
Non-amortized intangible assets
Carrying value of trade names	8,108	8,155
Ingal EPS/Ingal Civil Products
Non-amortized intangible assets
Carrying value of trade names	7,233	7,233
Walpar
Non-amortized intangible assets
Carrying value of trade names	4,300	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	17,490	16,472
Trade Names
Non-amortized intangible assets
Carrying value of trade names	$ 69,640	$ 68,723