EARNINGS PER SHARE (Details 2) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Impairment of goodwill & intangible assets									$ 0	$ 15,780	$ 0
Impairment of goodwill and intangible assets (in dollars per share)						$ 0.66
Net earnings attributable to Valmont Industries, Inc.	$ 35,747	$ 40,144	$ 41,397	$ 36,481	$ 17,662	$ 4,448	$ 32,960	$ 39,281	$ 153,769	$ 94,351	$ 116,240
Basic (in dollars per share)	$ 1.67	$ 1.86	$ 1.90	$ 1.67	$ 0.80	$ 0.20	$ 1.47	$ 1.74	$ 7.10	$ 4.23	$ 5.16
Blended tax rate (percent)					25.00%
Refinancing of long-term debt expense						$ 11,115			$ 11,115
Refinancing of long-term debt expense (in dollars per share)									$ 0.50
Deferred income tax expense					$ 20,372						$ 20,372
Deferred income tax expense (in dollars per share)					$ 0.90
Provision charge for deemed repatriation tax					$ 9,890
Provision charge for deemed repatriation tax (in dollars per share)					$ 0.44
Deferred expenses related to foreign withholding taxes and US state income taxes					$ 11,673				$ 1,279	$ (1,881)	$ 49,766
Deferred expenses related to foreign withholding taxes and US state income taxes (in dollars per share)					$ 0.51
Outstanding stock options with exercise prices exceeding the market price of common stock, excluded from the computation of diluted earnings per share (in shares)									130,704	406,806	0
Goodwill And Indefinite-lived Intangible Assets
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Impairment of goodwill & intangible assets									$ 14,736
Impairment of goodwill and intangible assets (in dollars per share)									$ 0.66
2018 Restructuring Plan
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Valmont Industries, Inc.									$ (37,779)
Basic (in dollars per share)									$ (1.68)
Disposed by sale | Donhad
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Valmont Industries, Inc.									$ 5,350
Basic (in dollars per share)									$ 0.24