| **Share-Based Compensation (Tables)**                                         | 9 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 EndedSeptember 30, Nine Months EndedSeptember 30,  2016 2015 2016 2015Stock and ESPP Options       Pre-tax compensation expense$18 $23 $54 $78Income tax expense (benefit)3 5 12 4Stock and ESPP option expense, net of income taxes$21 $28 $66 $82Restricted Stock Awards       Pre-tax compensation expense$630 $533 $1,829 $1,609Income tax benefit(221) (187) (640) (552)Restricted stock awards expense, net of income taxes$409 $346 $1,189 $1,057Total Share-Based Compensation       Pre-tax compensation expense$648 $556 $1,883 $1,687Income tax benefit(218) (182) (628) (548)Total share-based compensation expense, net of income taxes$430 $374 $1,255 $1,139 |
| Stock option activity under stock option plans                                | Stock option activity under the Corporation's stock option plans as of September 30, 2016 and changes during the nine months ended September 30, 2016, were as follows: Number ofSharesWeighted-Average Exercise PriceWeighted Average RemainingContractual Term(in Years)AggregateIntrinsicValueOutstanding at January 1, 2016442,012$19.99  Granted—  Exercised(22,385)$13.80  Canceled(52,953)$25.09  Outstanding September 30, 2016366,674$19.632.792,691,404Vested and Expected to Vest at September 30, 2016366,674$19.632.792,691,404Exercisable at September 30, 2016366,674$19.632.792,691,404                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Unvested RSAs outstanding                                                     | The following table summarizes information on unvested RSAs outstanding as of September 30, 2016: Number of SharesWeighted-AverageGrant Date Fair ValueUnvested RSAs at January 1, 2016354,504$19.65Granted121,034$23.61Vested(110,251)$15.46Forfeited(7,711)$21.96Unvested RSAs at September 30, 2016357,576$22.54                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |

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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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