|**Share-Based Compensation (Tables)**                                         | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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|**Disclosure of Compensation Related Costs, Share-based Payments [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Components of Share Based Compensation Awards                                 | The following table summarizes the components of the Corporation's share-based compensation awards recorded as expense:Three Months EndedMarch 31,20152014Stock and ESPP OptionsPre-tax compensation expense$27$44Income tax expense (benefit)(1)(3)Stock and ESPP option expense, net of income taxes$26$41Restricted Stock AwardsPre-tax compensation expense$490$461Income tax benefit(168)(161)Restricted stock awards expense, net of income taxes$322$300Total Share-Based CompensationPre-tax compensation expense$517$505Income tax benefit(169)(164)Total share-based compensation expense, net of income taxes$348$341
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|                                                                              | Three Months EndedMarch 31,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                              | 2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Stock and ESPP Options                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Pre-tax compensation expense                                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Income tax expense (benefit)                                                  | (1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Stock and ESPP option expense, net of income taxes                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Restricted Stock Awards                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Pre-tax compensation expense                                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Income tax benefit                                                            | (168                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Restricted stock awards expense, net of income taxes                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Total Share-Based Compensation                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Pre-tax compensation expense                                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Income tax benefit                                                            | (169                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Total share-based compensation expense, net of income taxes                   | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Stock Option Activity Under Stock Option Plans                                | Stock option activity under the Corporation's stock option plans as ofMarch 31, 2015and changes during thethree months ended March 31, 2015, were as follows:Number ofSharesWeighted-Average Exercise PriceWeighted Average RemainingContractual Term(in Years)AggregateIntrinsicValueOutstanding at January 1, 2015737,931$20.99GrantedExercised(23,373)$15.17Canceled(100)$28.25Outstanding March 31, 2015714,458$21.182.842,742,203Vested and Expected to Vest at March 31, 2015714,458$21.182.842,742,203Exercisable at March 31, 2015714,458$21.182.842,742,203                                                            
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|                                                                              | Number ofShares                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Outstanding at January 1, 2015                                                | 737,931                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Granted                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Exercised                                                                     | (23,373                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Canceled                                                                      | (100                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Outstanding March 31, 2015                                                    | 714,458                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Vested and Expected to Vest at March 31, 2015                                 | 714,458                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Exercisable at March 31, 2015                                                 | 714,458                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Unvested RSAs Outstanding                                                     | The following table summarizes information on unvested RSAs outstanding as ofMarch 31, 2015:Number of SharesWeighted-AverageGrant Date Fair ValueUnvested RSAs at January 1, 2015385,450$15.65Granted100,140$22.91Vested(126,531)$11.40Forfeited(1,487)$15.04Unvested RSAs at March 31, 2015357,572$19.19                                                                                                                                                                                                                                                                                                                       
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|                                                                              | Number of Shares                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Unvested RSAs at January 1, 2015                                              | 385,450                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Granted                                                                       | 100,140                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Vested                                                                        | (126,531                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Forfeited                                                                     | (1,487                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Unvested RSAs at March 31, 2015                                               | 357,572                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

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