v3.26.1
Form 5500, Schedule H, Part IV, Line 4i – Schedule of Assets (Held At End of Year) (Details) - Fastenal Company & Subsidiaries 401(k) and Employee Stock Ownership Plan
12 Months Ended
Dec. 31, 2025
USD ($)
Schedule of Asset Held for Investment [Line Items]  
Entity tax identification number 41-0948415
Plan number 001
Current Value $ 1,206,599,971
Investment, Identifier [Axis]: American Capital World  
Schedule of Asset Held for Investment [Line Items]  
Current Value 73,515,949
Investment, Identifier [Axis]: American Europacific Growth R6  
Schedule of Asset Held for Investment [Line Items]  
Current Value 40,758,694
Investment, Identifier [Axis]: BLF FedFund  
Schedule of Asset Held for Investment [Line Items]  
Current Value 591,795
Investment, Identifier [Axis]: Carillon Eagle Mid Cp. Grth. R6  
Schedule of Asset Held for Investment [Line Items]  
Current Value 16,316,711
Investment, Identifier [Axis]: FIAM Core Plus Commingled Cl. F  
Schedule of Asset Held for Investment [Line Items]  
Current Value 10,143,783
Investment, Identifier [Axis]: Fastenal Company Stock  
Schedule of Asset Held for Investment [Line Items]  
Current Value 316,565,240
Investment, Identifier [Axis]: Fidelity 500 Index Fund  
Schedule of Asset Held for Investment [Line Items]  
Current Value 176,782,428
Investment, Identifier [Axis]: Fidelity Mid Cap Index  
Schedule of Asset Held for Investment [Line Items]  
Current Value 20,077,295
Investment, Identifier [Axis]: Fidelity Small Cap Index Fund  
Schedule of Asset Held for Investment [Line Items]  
Current Value 17,771,230
Investment, Identifier [Axis]: Fidelity US Bond Index Fund  
Schedule of Asset Held for Investment [Line Items]  
Current Value 18,730,350
Investment, Identifier [Axis]: Invesco Stable Value Ret Cl. 1  
Schedule of Asset Held for Investment [Line Items]  
Current Value 22,812,882
Investment, Identifier [Axis]: John Hancock Disciplined Val. R6  
Schedule of Asset Held for Investment [Line Items]  
Current Value 56,716,585
Investment, Identifier [Axis]: Pending settlement fund  
Schedule of Asset Held for Investment [Line Items]  
Current Value 16,289
Investment, Identifier [Axis]: T Rowe Price Intl Discovery I  
Schedule of Asset Held for Investment [Line Items]  
Current Value 6,544,595
Investment, Identifier [Axis]: T Rowe Price Small Cap Stock I  
Schedule of Asset Held for Investment [Line Items]  
Current Value 13,872,174
Investment, Identifier [Axis]: Vanguard Federal Money Mkt. Inv.  
Schedule of Asset Held for Investment [Line Items]  
Current Value 16,765,483
Investment, Identifier [Axis]: Vanguard Target Retirement Inc  
Schedule of Asset Held for Investment [Line Items]  
Current Value 1,841,990
Investment, Identifier [Axis]: Vanguard Target Retiremt 2020  
Schedule of Asset Held for Investment [Line Items]  
Current Value 2,513,488
Investment, Identifier [Axis]: Vanguard Target Retiremt 2025  
Schedule of Asset Held for Investment [Line Items]  
Current Value 11,726,186
Investment, Identifier [Axis]: Vanguard Target Retiremt 2030  
Schedule of Asset Held for Investment [Line Items]  
Current Value 28,010,087
Investment, Identifier [Axis]: Vanguard Target Retiremt 2035  
Schedule of Asset Held for Investment [Line Items]  
Current Value 40,681,977
Investment, Identifier [Axis]: Vanguard Target Retiremt 2040  
Schedule of Asset Held for Investment [Line Items]  
Current Value 46,738,126
Investment, Identifier [Axis]: Vanguard Target Retiremt 2045  
Schedule of Asset Held for Investment [Line Items]  
Current Value 64,560,490
Investment, Identifier [Axis]: Vanguard Target Retiremt 2050  
Schedule of Asset Held for Investment [Line Items]  
Current Value 64,780,913
Investment, Identifier [Axis]: Vanguard Target Retiremt 2055  
Schedule of Asset Held for Investment [Line Items]  
Current Value 51,731,935
Investment, Identifier [Axis]: Vanguard Target Retiremt 2060  
Schedule of Asset Held for Investment [Line Items]  
Current Value 51,094,521
Investment, Identifier [Axis]: Vanguard Target Retiremt 2065  
Schedule of Asset Held for Investment [Line Items]  
Current Value 31,146,228
Investment, Identifier [Axis]: Vanguard Target Retiremt 2070  
Schedule of Asset Held for Investment [Line Items]  
Current Value $ 3,792,547