Document and Entity Information - shares	3 Months Ended
	Mar. 30, 2019	Apr. 26, 2019
Document and Entity Information
Entity Registrant Name	VALMONT INDUSTRIES INC
Entity Central Index Key	0000102729
Document Type	10-Q
Document Period End Date	Mar. 30, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-29
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		21,856,613
Entity Emerging Growth Company	false
Entity Small Business	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1