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Stock-Based Compensation Plans - Restricted Stock Activity (Details) - $ / shares
3 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Restricted stock    
Restricted stock shares    
Equity instruments outstanding at the beginning of the period (in shares) 157,066  
Granted (in shares) 78,082 92,975
Vested (in shares) (70,596)  
Forfeited (in shares) (1,120)  
Equity instruments outstanding at the end of the period (in shares) 163,432  
Restricted stock shares weighted average grant date fair value per share    
Equity instruments outstanding at the beginning of the period (in dollars per share) $ 192.90  
Grant date fair value per share (in dollars per share) 236.17  
Vested (in dollars per share) 195.83  
Forfeited (in dollars per share) 219.75  
Equity instruments outstanding at the end of the period (in dollars per share) $ 212.12  
Restricted Stock Converted From Performance Shares    
Restricted stock shares    
Equity instruments outstanding at the beginning of the period (in shares) 74,627  
Granted (in shares) 0  
Vested (in shares) (47,335)  
Forfeited (in shares) (28)  
Equity instruments outstanding at the end of the period (in shares) 27,264