NET EARNINGS PER SHARE - Reconciliation of earnings and share amounts to compute basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 28, 2025	Dec. 27, 2025	Dec. 28, 2024	Dec. 30, 2023
NET EARNINGS PER SHARE
Net Income (Loss)		$ 350,273	$ 348,259	$ 150,849
Change in redemption value of redeemable noncontrolling interests	$ (26,243)	(15,489)		(7,374)
Net earnings attributable to Valmont Industries, Inc. including change in redemption value of redeemable noncontrolling interests		334,784	348,259	143,475
Net earnings attributable to Valmont Industries, Inc. including change in redemption value of redeemable noncontrolling interests		$ 334,784	$ 348,259	$ 143,475
Weighted average shares outstanding (in thousands):
Basic (in shares)		19,795,000	20,122,000	20,956,000
Dilutive effect of various stock awards (in shares)		142,000	139,000	203,000
Diluted (in shares)		19,937,000	20,261,000	21,159,000
Net earnings attributable to Valmont Industries, Inc. per share:
Basic (in dollars per share)		$ 16.91	$ 17.31	$ 6.85
Dilutive effect of various stock awards (in dollars per share)		(0.12)	(0.12)	(0.07)
Diluted (in dollars per share)		$ 16.79	$ 17.19	$ 6.78
Outstanding stock options with exercise prices exceeding the market price of common stock, excluded from the computation of diluted earnings per share (in shares)		22,216	44,620	127,774