Earnings Per Common Share - Summary of Computation of Basic and Diluted Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income available to common shareholders	$ 77,227	$ 75,205	$ 76,284
Denominator:
Weighted-average shares	15,412,365	15,407,078	15,400,155
Effect of dilutive securities – stock options and warrants	0	1,063	1,291
Earnings per common share:	15,412,365	15,408,141	15,401,446
Earnings per common share:
Basic earnings per common share	$ 5.01	$ 4.88	$ 4.95
Diluted earnings per common share	$ 5.01	$ 4.88	$ 4.95

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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