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Stock-based Compensation (Changes in Non-vested Restricted Stock Units) (Details) - Restricted Stock Units [Member] - $ / shares
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Shares      
Undistributed as of beginning of period (in shares) 136,000.0    
Granted (in shares) 50,300    
Distributed (in shares) (47,100)    
Forfeited (in shares) (4,100)    
Undistributed as of end of period (in shares) 135,100 136,000.0  
Weighted- Average Grant Date Fair Value per Share      
Undistributed as of beginning of period (in usd per share) $ 237.45    
Granted (in usd per share) 315.70 $ 265.96 $ 247.02
Distributed (in usd per share) 205.54    
Forfeited (in usd per share) 232.39    
Undistributed as of end of period (in usd per share) $ 277.85 $ 237.45