| **Share-Based Compensation (Tables)**                                         | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| **Disclosure of Compensation Related Costs, Share-based Payments [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Assumptions Used In 2012 Black Scholes Model                                  | The estimated fair value of the stock options granted during 2014, 2013, and 2012 was calculated using a Black-Scholes option pricing model.  The following summarizes the assumptions used in the Black-Scholes model: 2014 2013 2012 Risk-free interest rate2.41% 1.25% 1.36% Expected price volatility45.05% 45.68% 46.22% Dividend yield2.73% 2.96% 3.29% Forfeiture rate5.46% 4.73% 4.77% Weighted-average expected life, until exercise7.74years7.27years7.20years                                                                                                                                                                                                                                                       |
| Components of Share Based Compensation Awards                                 | The following table summarizes the components of the Corporation's share-based compensation awards recorded as expense:Year EndedDecember 31,  Year EndedDecember 31, Year EndedDecember 31,  2014 2013 2012Stock and ESPP Options   Pre-tax compensation expense$237$253$284Income tax benefit(47)(16)(23)Stock and ESPP option expense, net of income taxes$190$237$261Restricted Stock Awards   Pre-tax compensation expense$1,940$1,520$1,208Income tax benefit(679)(531)(428)Restricted stock awards expense, net of income taxes$1,261$989$780Total Share-Based Compensation:   Pre-tax compensation expense$2,177$1,773$1,492Income tax benefit(726)(547)(451)Total share-based compensation expense, net of income taxes$1,451$1,226$1,041 |
| Stock Option Activity Under Stock Option Plans                                | Stock option activity under the Corporation's stock option plans, as of December 31, 2014, and changes during the year ended December 31, 2014, were as follows:  Number ofSharesWeighted-AverageExercise PriceWeighted AverageRemaining ContractualTerm (in Years)AggregateIntrinsic ValueOutstanding at January 1, 2014958,786$21.32  Granted13,500$21.65  Exercised(41,249)$12.21Canceled(193,106)$24.42  Outstanding December 31, 2014737,931$20.993.082,645,356Vested and Expected to Vest at December 31, 2014737,931$20.993.082,645,356Exercisable at December 31, 2014715,431$21.052.902,563,636                                                                                                                                                               |
| Unvested RSAs Outstanding                                                     | The following table summarizes information on unvested RSAs outstanding as of December 31, 2014: Number ofSharesWeighted-AverageGrant Date Fair ValueUnvested RSAs at January 1, 2014429,002$12.51Granted98,611$20.54Forfeited(9,717)$15.78Vested(132,446)$9.16Unvested RSAs at December 31, 2014385,450$15.65                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |

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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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| - Definition
Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.
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