| **Net Income Per Share**          | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| **Earnings Per Share [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Net Income Per Share              | NET INCOME PER SHAREBasic net income per share is computed by dividing net income by the weighted-average shares outstanding during the reporting period. Diluted net income per share is computed by dividing net income by the combination of all dilutive common share equivalents, comprised of shares issuable under the Corporation’s share-based compensation plans, and the weighted-average shares outstanding during the reporting period.Dilutive common share equivalents include the dilutive effect of in-the-money share-based awards, which are calculated based on the average share price for each period using the treasury stock method. Under the treasury stock method, the exercise price of share-based awards, the amount of compensation expense, if any, for future service that the Corporation has not yet recognized, and the amount of estimated tax benefits that would be recorded in additional paid-in capital when share-based awards are exercised, are assumed to be used to repurchase common stock in the current period.The following table reconciles basic and diluted net income per share for the years indicated: 2016 2015 2014   Weighted-Average Shares     Weighted-Average Shares     Weighted-Average Shares  Basic net income per share:                 Net income available to common stockholders$81,051 40,767,343 $1.99 $65,384 37,816,399 $1.73 $60,162 36,266,356 $1.66Effect of dilutive stock options and warrants  245,790     271,834     288,253  Diluted net income per share:                 Net income available to common stockholders$81,051 41,013,133 $1.98 $65,384 38,088,233 $1.72 $60,162 36,554,609 $1.65  Options to purchase 51,949, 286,119, and 543,514 shares of common stock with weighted average exercise prices of $19.26, $19.99, and $20.99 at December 31, 2016, 2015 and 2014 respectively, were excluded from the computation of diluted net income per share because the options exercise price was greater than the average market price of the common stock. |

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| - Definition
The entire disclosure for earnings per share.
+ References
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