| **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, 20142013Stock and ESPP Options  Pre-tax compensation expense$44$38Income tax expense (benefit)(3)(2)Stock and ESPP option expense, net of income taxes$41$36Restricted Stock Awards  Pre-tax compensation expense$461$336Income tax benefit(161)(117)Restricted stock awards expense, net of income taxes$300$219Total Share-Based Compensation  Pre-tax compensation expense$505$374Income tax benefit(164)(119)Total share-based compensation expense, net of income taxes$341$255 |
| Stock Option Activity Under Stock Option Plans                                | Stock option activity under the Corporation's stock option plans as of March 31, 2014 and changes during the three months ended March 31, 2014, were as follows: Number ofSharesWeighted-Average Exercise PriceWeighted Average RemainingContractual Term(in Years)AggregateIntrinsicValueOutstanding at January 1, 2014958,786$21.32  Granted  Exercised(25,050)$10.88  Canceled1,815$22.15  Outstanding March 31, 2014935,551$21.602.972,401,422Vested and Expected to Vest at March 31, 2014935,551$21.602.972,401,422Exercisable at March 31, 2014926,551$21.662.912,344,542                                    |
| Unvested RSAs Outstanding                                                     | The following table summarizes information on unvested RSAs outstanding as of March 31, 2014: Number of SharesWeighted-AverageGrant Date Fair ValueUnvested RSAs at January 1, 2014429,002$12.51Granted84,792$20.43Vested(105,509)$12.50Forfeited(1,970)$9.07Unvested RSAs at March 31, 2014406,315$15.06                                                                                                                                                                                                                                                                                                                                                        |

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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.
+ References
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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.
+ References
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