EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020
Basic EPS
Net earnings attributable to Valmont Industries, Inc.	$ 51,650	$ 39,342	$ 168,774	$ 104,878
Weighted average shares outstanding (in shares)	21,175,000	21,309,000	21,182,000	21,358,000
Per share amount basic (in dollars per share)	$ 2.44	$ 1.85	$ 7.97	$ 4.91
Dilutive Effect of Stock Options
Dilutive Effect of Stock Options	$ 0	$ 0	$ 0	$ 0
Dilutive effect of stock options number of shares (in shares)	377,000	107,000	301,000	95,000
Dilutive effect of stock options (in dollars per share)	$ (0.04)	$ (0.01)	$ (0.11)	$ (0.02)
Diluted EPS
Diluted EPS	$ 51,650	$ 39,342	$ 168,774	$ 104,878
Shares outstanding dilutive (in shares)	21,552,000	21,416,000	21,483,000	21,453,000
Per share amount diluted (in dollars per share)	$ 2.40	$ 1.84	$ 7.86	$ 4.89
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)			0	296,966