EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Basic EPS
Net earnings attributable to Valmont Industries, Inc.	$ 22,607	$ 39,719	$ 65,536	$ 75,823
Weighted average shares outstanding (in shares)	21,312,000	21,734,000	21,383,000	21,810,000
Per share amount basic (in dollars per share)	$ 1.06	$ 1.83	$ 3.06	$ 3.48
Dilutive Effect of Stock Options
Dilutive Effect of Stock Options	$ 0	$ 0	$ 0	$ 0
Dilutive effect of stock options number of shares (in shares)	81,000	97,000	88,000	87,000
Dilutive effect of stock options (in dollars per share)	$ 0	$ (0.01)	$ (0.01)	$ (0.02)
Diluted EPS
Diluted EPS	$ 22,607	$ 39,719	$ 65,536	$ 75,823
Shares outstanding dilutive (in shares)	21,393,000	21,831,000	21,471,000	21,897,000
Per share amount diluted (in dollars per share)	$ 1.06	$ 1.82	$ 3.05	$ 3.46
Antidilutive Securities
Outstanding stock options with exercise prices exceeding the market price of common stock, excluded from the computation of diluted earnings per share (in shares)			296,490	297,170