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Employee Benefit and Deferred Compensation Plans - Summary of the Changes in Stock Options (Details) - $ / shares
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Shares    
Options outstanding at beginning of period (shares) 89,750  
Granted (shares) 0 0
Exercised (shares) (27,000)  
Forfeited (shares) 0  
Options outstanding at end of period (shares) 62,750  
Weighted Average Exercise Price    
Options outstanding at beginning of period (usd per share) $ 15.67  
Granted (usd per share) 0.00  
Exercised (usd per share) 15.76  
Forfeited (usd per share) 0.00  
Options outstanding at end of period (usd per share) $ 15.64