Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share Basic [Abstract]
Net income available to common shareholders - basic	$ 15,481	$ 16,639	$ 29,005	$ 40,896
Basic weighted average common shares	19,162,049	19,096,718	19,156,250	19,077,328
Basic earnings per common share	$ 0.81	$ 0.87	$ 1.51	$ 2.14
Net income available to common shareholders - diluted	$ 15,481	$ 16,639	$ 29,005	$ 40,896
Weighted average common shares	19,162,049	19,096,718	19,156,250	19,077,328
Stock options and restricted stock	65,911	88,266	71,747	101,565
Diluted weighted average common shares	19,227,960	19,184,984	19,227,997	19,178,893
Diluted earnings per common share	$ 0.81	$ 0.87	$ 1.51	$ 2.13

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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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

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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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