Document and Entity Information - USD ($)	12 Months Ended
	Dec. 29, 2018	Feb. 21, 2019	Jun. 30, 2018
Document and Entity Information
Entity Registrant Name	VALMONT INDUSTRIES INC
Entity Central Index Key	0000102729
Document Type	10-K
Document Period End Date	Dec. 29, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-29
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3,233,462,981
Entity Common Stock, Shares Outstanding		21,941,622
Smaller Reporting Company	false
Emerging Growth Company	false
Shell Company	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY