Cover
| Cover | Feb. 21, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 21, 2020 |
| Entity File Number | 1-31429 |
| Entity Registrant Name | Valmont Industries, Inc. |
| Entity Central Index Key | 0000102729 |
| Entity Tax Identification Number | 47-0351813 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | One 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 |