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ACQUISITIONS - Narrative (Details) - USD ($) $ in Thousands					1 Months Ended		3 Months Ended
ACQUISITIONS - Narrative (Details) - USD ($) $ in Thousands	May 29, 2020	May 13, 2019	Feb. 11, 2019	Dec. 31, 2018	Feb. 29, 2020	Apr. 30, 2019	Sep. 26, 2020	Mar. 28, 2020	Dec. 28, 2019
Business Acquisition [Line Items]
Goodwill							$ 421,947		$ 428,864
Energia Solar do Brasil
Business Acquisition [Line Items]
Percentage acquired	55.00%
Cash paid in acquisition	$ 4,308
Contingent consideration liability, current	646
Goodwill	3,341
Connect-It Wireless, Inc.
Business Acquisition [Line Items]
Cash paid in acquisition		$ 6,034
Goodwill		3,299
United Galvanizing
Business Acquisition [Line Items]
Contingent consideration liability, current			$ 2,000
Consideration transfered			$ 28,000
Settled representations and warranties							$ 1,522
Larson Camouflage
Business Acquisition [Line Items]
Consideration transfered				$ 34,562
Settled representations and warranties								$ 3,481
Contingent consideration liability, as percent of purchase price (percent)				10.00%
AgSense
Business Acquisition [Line Items]
Percentage acquired					49.00%		100.00%
Consideration transfered					$ 43,983
Holdback payment							$ 2,200
Deferred tax asset recognized							$ 7,700
Convert Italia S.p.A
Business Acquisition [Line Items]
Percentage acquired					16.00%
Consideration transfered					$ 11,750
Convert Italia S.p.A \| Minority Interest Owner
Business Acquisition [Line Items]
Percentage not owned by the Company					25.00%
Valmont SM
Business Acquisition [Line Items]
Percentage acquired						4.80%
Consideration transfered						$ 4,763
Customer Relationships \| Energia Solar do Brasil
Business Acquisition [Line Items]
Intangible assets acquired	$ 3,718
Useful life	8 years
Customer Relationships \| Connect-It Wireless, Inc.
Business Acquisition [Line Items]
Intangible assets acquired		$ 828