Earnings Per Common Share - Summary of Computation of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income available to common shareholders	$ 81,012	$ 83,957	$ 76,869
Denominator:
Weighted-average common shares outstanding	15,364,281	15,394,971	15,412,365
Effect of dilutive securities – performance based restricted stock units	40,459	18,861	0
Earnings per common share:	15,404,740	15,413,832	15,412,365
Earnings per common share:
Basic earnings per common share	$ 5.27	$ 5.45	$ 4.99
Diluted earnings per common share	$ 5.26	$ 5.45	$ 4.99

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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