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Earnings Per Common Share and Share Awards (Details) - USD ($)
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Earnings Per Common Share And Share Awards [Line Items]      
Incremental dilutive potential common shares, calculated using treasury stock method (in shares) 5,439 5,774 20,459
Anti-dilutive shares excluded from computation of diluted earnings per share 0 0 0
SARs and options vesting period 1 year    
Intrinsic values of options exercised $ 104,000 $ 82,000 $ 3,486,000
Options and SARs vested 4,500    
Fair value of options and SARs vested $ 137,762    
Weighted-average fair values for SARs issued (dollars per share) $ 31.16 $ 28.98 $ 27.55
Compensation expense relating to SARs or options vesting $ 138,000 $ 121,000 $ 84,000
Total unrecognized compensation cost related to unvested share-based compensation arrangements granted under stock award plans $ 35,000    
Weighted-average period of unrecognized compensation cost recognition 3 months    
Number of stock options or SARs granted where exercise price was less than market price on date of grant 0    
Minimum      
Earnings Per Common Share And Share Awards [Line Items]      
Annual rate at which stock appreciation rights and options are exercisable and vest 10.00%    
SARs and options expiration period 5 years    
Maximum      
Earnings Per Common Share And Share Awards [Line Items]      
Maximum shares of Company stock to be granted to key employees or directors 500,000    
Annual rate at which stock appreciation rights and options are exercisable and vest 20.00%    
SARs and options expiration period 10 years