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Stock Plans (Narrative) (Details)
3 Months Ended 12 Months Ended
Feb. 05, 2019
$ / shares
shares
Mar. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
item
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of active share-based compensation plans | item     2      
Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Non-option shares granted     12,901 19,250 13,224  
Stock-Settled Stock Appreciation Rights (SSARs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares granted     11,073 38,941 24,346  
Vesting period     3 years      
Options exercised     3,059 3,051  
Options exercised, intrinsic value | $     $ 10,631 $ 12,288    
Options exercised, realized tax deduction | $     108,134 122,969    
Options exercised, tax benefit | $     $ 22,708 $ 25,823    
Options outstanding     97,264 89,250 53,360 29,014
Employee Stock Option [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares granted        
Options exercised   750   750 21,750  
Options exercised, price per share | $ / shares   $ 18.50   $ 18.50 $ 19.14  
Options exercised, grant date intrinsic value | $   $ 2,585     $ 79,715  
Options exercised, realized tax deduction | $   22,875     363,392  
Options exercised, tax benefit | $   $ 4,804     $ 123,553  
Options outstanding     0 750 22,500
2012 Stock Incentive Plans [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Award expiration date     Dec. 31, 2022      
Director Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized     750,000      
Vesting period     3 years 3 years 2 years  
Director Plan [Member] | Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Non-option shares granted 5,600   5,600 8,400 8,400  
Omnibus Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized     750,000      
Omnibus Plan [Member] | Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Term used to determine historical volatility 5 years          
Grant date stock price | $ / shares $ 59.70          
Discount rate 8.393%          
Interest rate 2.494%          
Volatility rate 19.411%          
Omnibus Plan [Member] | Stock-Settled Stock Appreciation Rights (SSARs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares granted 11,073          
Expected term 10 years   10 years      
Dividend rate 1.628%          
Grant date fair value stock price | $ / shares $ 16.79          
Interest rate 2.692%          
Volatility rate 23.732%          
Long-Term Incentive Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Vesting period     3 years      
Performance period     3 years      
Long-Term Incentive Plan [Member] | Senior Officers and Managers [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Performance period     1 year      
Long-Term Incentive Plan [Member] | Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Holding period     2 years      
Employee Stock Purchase Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized     165,000      
Number of shares issued     81,019      
Dividend Reinvestment Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized     750,000      
Dividend reinvestment plan, shares available for issuance     591,730      
Award Date One [Member] | Omnibus Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Vesting period     3 years 3 years 3 years  
Award Date One [Member] | Omnibus Plan [Member] | Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Non-option shares granted 7,251   7,251 10,800 4,749  
Vesting period 3 years          
Holding period 2 years          
Term used to determine historical volatility 5 years          
Treasury yield 5 years