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ACQUISITIONS - Narrative (Details) - USD ($) $ in Thousands				1 Months Ended
ACQUISITIONS - Narrative (Details) - USD ($) $ in Thousands	May 13, 2019	Feb. 11, 2019	Dec. 31, 2018	Feb. 29, 2020	Apr. 30, 2019	Mar. 28, 2020	Dec. 28, 2019
Business Acquisition [Line Items]
Goodwill						$ 422,514	$ 428,864
Connect-It Wireless, Inc.
Business Acquisition [Line Items]
Cash paid in acquisition	$ 6,034
Goodwill	3,299
United Galvanizing
Business Acquisition [Line Items]
Cash paid in acquisition		$ 26,000
Goodwill		12,374
Consideration transfered		28,000
Contingent consideration liability, current		2,000
Settled representations and warranties						$ 1,522
Property, plant, and equipment acquired		10,987
Larson Camouflage
Business Acquisition [Line Items]
Cash paid in acquisition			$ 31,106
Goodwill			15,346
Consideration transfered			34,562
Settled representations and warranties			3,481
Intangible assets acquired			16,223
Property, plant, and equipment acquired			$ 1,151
Contingent consideration liability, as percent of purchase price (percent)			10.00%
Convert Italia S.p.A
Business Acquisition [Line Items]
Consideration transfered				$ 11,750
Percentage acquired				16.00%
Convert Italia S.p.A \| Minority Interest Owner
Business Acquisition [Line Items]
Percentage not owned by the Company				25.00%
AgSense
Business Acquisition [Line Items]
Consideration transfered				$ 44,284
Contingent consideration liability, current				$ 2,500
Percentage acquired				49.00%
Valmont SM
Business Acquisition [Line Items]
Consideration transfered					$ 4,763
Percentage acquired					4.80%
Customer Relationships \| Connect-It Wireless, Inc.
Business Acquisition [Line Items]
Intangible assets acquired	$ 828
Customer Relationships \| United Galvanizing
Business Acquisition [Line Items]
Intangible assets acquired		$ 3,170
Useful life		10 years
Customer Relationships \| Larson Camouflage
Business Acquisition [Line Items]
Useful life			12 years
Trade Names \| United Galvanizing
Business Acquisition [Line Items]
Intangible assets acquired		$ 894