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Stockholders' Equity - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
 6 Months Ended
Jul. 13, 2015
Jun. 30, 2015
Jun. 30, 2014
Schedule of Shareholders' Equity [Line Items]      
Options vesting and exercisable period, maximum   8 years  
Options termination period   9 years  
Total stock-based compensation expense for the Fastenal stock option plan   $ 3,441 $ 3,000
Total unrecognized stock-based compensation expense   $ 17,707  
Weighted average period over which total unrecognized stock-based compensation expense will be recognized   5 years 14 days  
Subsequent Event [Member]      
Schedule of Shareholders' Equity [Line Items]      
Dividend declared date Jul. 13, 2015    
Dividend declared per share $ 0.28    
Dividend payment date Aug. 25, 2015    
Dividend payable record date Jul. 28, 2015