v3.26.1
FAIR VALUE MEASUREMENTS - Fair value hierarchy - Plan's investments at fair value (Details) - EMPLOYEE RETIREMENT SAVINGS PLAN - USD ($)
Dec. 31, 2025
Dec. 31, 2024
FAIR VALUE MEASUREMENTS    
Total investments, at fair value $ 751,483,222 $ 651,809,749
Stable value fund    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 21,740,195 22,376,223
Common collective trusts    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 528,035,568 457,433,164
Mutual funds    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 163,411,585 139,845,497
Valmont Industries, Inc. common stock    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 38,295,874 32,154,865
Fair value hierarchy    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 201,707,459 172,000,362
Fair value hierarchy | Mutual funds    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 163,411,585 139,845,497
Fair value hierarchy | Valmont Industries, Inc. common stock    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 38,295,874 32,154,865
Level 1    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 201,707,459 172,000,362
Level 1 | Mutual funds    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 163,411,585 139,845,497
Level 1 | Valmont Industries, Inc. common stock    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 38,295,874 32,154,865
Net asset value    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 549,775,763 479,809,387
Net asset value | Stable value fund    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value 21,740,195 22,376,223
Net asset value | Common collective trusts    
FAIR VALUE MEASUREMENTS    
Total investments, at fair value $ 528,035,568 $ 457,433,164