| **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,  2016 2015 Stock and ESPP Options    Pre-tax compensation expense$15 $27 Income tax expense (benefit) (1) Stock and ESPP option expense, net of income taxes$15 $26 Restricted Stock Awards    Pre-tax compensation expense$578 $490 Income tax benefit(202) (168) Restricted stock awards expense, net of income taxes$376 $322 Total Share-Based Compensation    Pre-tax compensation expense$593 $517 Income tax benefit(202) (169) Total share-based compensation expense, net of income taxes$391 $348  |
| Stock option activity under stock option plans                                | Stock option activity under the Corporation's stock option plans as of March 31, 2016 and changes during the three months ended March 31, 2016, were as follows: Number ofSharesWeighted-Average Exercise PriceWeighted Average RemainingContractual Term(in Years)AggregateIntrinsicValueOutstanding at January 1, 2016442,012$19.99  Granted—  Exercised(6,700)$10.80  Canceled(49,500)$25.14  Outstanding March 31, 2016385,812$19.493.231,992,120Vested and Expected to Vest at March 31, 2016385,812$19.493.231,992,120Exercisable at March 31, 2016385,812$19.493.231,992,120                                                                                                                                                                                                |
| Unvested RSAs outstanding                                                     | The following table summarizes information on unvested RSAs outstanding as of March 31, 2016: Number of SharesWeighted-AverageGrant Date Fair ValueUnvested RSAs at January 1, 2016354,504$19.65Granted110,623$23.41Vested(101,984)$15.32Forfeited(419)$21.60Unvested RSAs at March 31, 2016362,724$22.31                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |

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| - Definition
Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed.
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| - Definition
Tabular disclosure of the changes in outstanding nonvested restricted stock units.
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| - Definition
Tabular disclosure of the number and weighted-average exercise prices (or conversion ratios) for share options (or share units) that were outstanding at the beginning and end of the year, vested and expected to vest, exercisable or convertible at the end of the year, and the number of share options or share units that were granted, exercised or converted, forfeited, and expired during the year.
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