Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income available to common shareholders	$ 27,949	$ 23,706
Denominator:
Basic weighted average shares outstanding	29,363,210	29,697,722
Effect of dilutive securities:
Diluted weighted average shares outstanding	29,561,406	29,910,292
Basic earnings per share	$ 0.95	$ 0.80
Diluted earnings per share	$ 0.95	$ 0.79
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities	100,585	148,047
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities	97,611	64,523

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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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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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