EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Basic EPS
Net earnings attributable to Valmont Industries, Inc.	$ 40,144	$ 4,448	$ 118,022	$ 76,689
Weighted average shares outstanding (in shares)	21,556,000	22,215,000	21,725,000	22,421,000
Per share amount basic (in dollars per share)	$ 1.86	$ 0.20	$ 5.43	$ 3.42
Dilutive Effect of Stock Options
Dilutive Effect of Stock Options	$ 0	$ 0	$ 0	$ 0
Dilutive effect of stock options number of shares (in shares)	128,000	137,000	101,000	153,000
Dilutive effect of stock options (in dollars per share)	$ 0.01	$ 0	$ (0.02)	$ (0.02)
Diluted EPS
Diluted EPS	$ 40,144	$ 4,448	$ 118,022	$ 76,689
Shares outstanding dilutive (in shares)	21,684,000	22,352,000	21,826,000	22,574,000
Per share amount diluted (in dollars per share)	$ 1.85	$ 0.20	$ 5.41	$ 3.40
Impact on net income (loss) available for common stockholders	$ (40,144)	$ (4,448)	$ (118,022)	$ (76,689)
Impact effect on earnings per share basic (in dollars per share)	$ (1.86)	$ (0.20)	$ (5.43)	$ (3.42)
Impact effect on net income (loss) available to common stockholders, diluted (in dollars per share)	$ (40,144)	$ (4,448)	$ (118,022)	$ (76,689)
Impact effect on earnings per share diluted (in dollars per share)	$ (1.85)	$ (0.20)	$ (5.41)	$ (3.40)
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)			177,153	190,021