EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Basic EPS
Net earnings attributable to Valmont Industries, Inc.	$ 39,342	$ 38,045	$ 104,878	$ 113,868
Weighted average shares outstanding (in shares)	21,309,000	21,556,000	21,358,000	21,725,000
Per share amount basic (in dollars per share)	$ 1.85	$ 1.76	$ 4.91	$ 5.24
Dilutive Effect of Stock Options
Dilutive Effect of Stock Options	$ 0	$ 0	$ 0	$ 0
Dilutive effect of stock options number of shares (in shares)	107,000	128,000	95,000	101,000
Dilutive effect of stock options (in dollars per share)	$ (0.01)	$ (0.01)	$ (0.02)	$ (0.02)
Diluted EPS
Diluted EPS	$ 39,342	$ 38,045	$ 104,878	$ 113,868
Shares outstanding dilutive (in shares)	21,416,000	21,684,000	21,453,000	21,826,000
Per share amount diluted (in dollars per share)	$ 1.84	$ 1.75	$ 4.89	$ 5.22
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)			296,966	177,153