| Document and Entity Information Document | Apr. 21, 2021 | Oct. 21, 2020 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Jul. 21, 2021 | |
| Entity Registrant Name | Valmont Industries, Inc. | |
| Entity Central Index Key | 0000102729 | |
| Amendment Flag | false | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 1-31429 | |
| Entity Tax Identification Number | 47-0351813 | |
| Entity Address, Address Line One | 15000 Valmont Plaza | |
| Entity Address, City or Town | Omaha | |
| Entity Address, State or Province | NE | |
| Entity Address, Postal Zip Code | 68154 | |
| City Area Code | 402 | |
| Local Phone Number | 963-1000 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Title of 12(b) Security | Common Stock, $1.00 par value | |
| Trading Symbol | VMI | |
| Security Exchange Name | NYSE | |
| Entity Emerging Growth Company | false |
