EARNINGS PER SHARE - Reconciliation of earnings and share amounts to compute basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 27, 2025	Jun. 28, 2025	Sep. 28, 2024	Sep. 27, 2025	Sep. 28, 2024
EARNINGS PER SHARE
Net earnings (loss) attributable to Valmont Industries, Inc.	$ 99,031		$ 83,068	$ 182,272	$ 270,606
Change in redemption value of redeemable noncontrolling interest		$ (26,243)		(26,243)
Net earnings (loss) attributable to Valmont Industries, Inc. including change in redemption value of redeemable noncontrolling interests	$ 99,031		$ 83,068	$ 156,029	$ 270,606
Weighted average shares outstanding (in thousands):
Basic (in shares)	19,736		20,092	19,864	20,152
Dilutive effect of various stock awards (in shares)	140		142	137	131
Diluted (in shares)	19,876		20,234	20,001	20,283
Net earnings (loss) attributable to Valmont Industries, Inc. per share:
Basic (in dollars per share)	$ 5.02		$ 4.13	$ 7.85	$ 13.43
Dilutive effect of various stock awards (in dollars per share)	(0.04)		(0.02)	(0.05)	(0.09)
Diluted (in dollars per share)	$ 4.98		$ 4.11	$ 7.8	$ 13.34