EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Basic EPS
Net earnings attributable to Valmont Industries, Inc.	$ (3,611,000)	$ 35,208,000	$ 45,664,000	$ 38,979,000	$ 70,064,000	$ 28,173,000	$ 42,026,000	$ 32,969,000	$ 116,240,000	$ 173,232,000	$ 40,117,000
Shares outstanding basic (in shares)									22,520	22,562	23,288
Per share amount basic (in dollars per share)	$ (0.16)	$ 1.56	$ 2.03	$ 1.73	$ 3.12	$ 1.25	$ 1.86	$ 1.45	$ 5.16	$ 7.68	$ 1.72
Dilutive Effect of Stock Options
Dilutive Effect of Stock Options									$ 0	$ 0	$ 0
Dilutive effect of stock options number of shares (in shares)									218	147	117
Dilutive effect of stock options (in dollars per share)									$ 0.05	$ 0.05	$ 0.01
Diluted EPS
Diluted EPS									$ 116,240,000	$ 173,232,000	$ 40,117,000
Shares outstanding dilutive (in shares)									22,738	22,709	23,405
Per share amount diluted (in dollars per share)	$ (0.16)	$ 1.55	$ 2.01	$ 1.72	$ 3.10	$ 1.24	$ 1.85	$ 1.45	$ 5.11	$ 7.63	$ 1.71