v3.26.1
Fair Value Measurements (Details) - Fastenal Company & Subsidiaries 401(k) and Employee Stock Ownership Plan - USD ($)
Dec. 31, 2025
Dec. 31, 2024
Investments at Fair Value [Line Items]    
Total investments at fair value $ 1,206,599,971 $ 1,039,093,227
Total    
Investments at Fair Value [Line Items]    
Total investments at fair value 1,206,599,971 1,039,093,227
Total | Mutual funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 458,459,578 403,598,461
Total | Fastenal Company common stock    
Investments at Fair Value [Line Items]    
Total investments at fair value 316,565,240 285,153,120
Total | Stable value fund    
Investments at Fair Value [Line Items]    
Total investments at fair value 22,812,882 22,628,532
Total | Common/collective trust funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 408,762,271 327,713,114
Level 1    
Investments at Fair Value [Line Items]    
Total investments at fair value 775,024,818 688,751,581
Level 1 | Mutual funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 458,459,578 403,598,461
Level 1 | Fastenal Company common stock    
Investments at Fair Value [Line Items]    
Total investments at fair value 316,565,240 285,153,120
Level 1 | Stable value fund    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 1 | Common/collective trust funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 2    
Investments at Fair Value [Line Items]    
Total investments at fair value 431,575,153 350,341,646
Level 2 | Mutual funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 2 | Fastenal Company common stock    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 2 | Stable value fund    
Investments at Fair Value [Line Items]    
Total investments at fair value 22,812,882 22,628,532
Level 2 | Common/collective trust funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 408,762,271 327,713,114
Level 3    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 3 | Mutual funds    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 3 | Fastenal Company common stock    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 3 | Stable value fund    
Investments at Fair Value [Line Items]    
Total investments at fair value 0 0
Level 3 | Common/collective trust funds    
Investments at Fair Value [Line Items]    
Total investments at fair value $ 0 $ 0