Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net income available to common shareholders	$ 23,279	$ 18,715	$ 46,681	$ 36,268
Denominator:
Basic weighted average shares outstanding	29,264,362	31,735,333	29,481,042	31,709,645
Effect of dilutive securities:
Diluted weighted average shares outstanding	29,423,845	32,142,939	29,642,287	32,119,026
Basic earnings per share	$ 0.80	$ 0.59	$ 1.58	$ 1.14
Diluted earnings per share	$ 0.79	$ 0.58	$ 1.57	$ 1.13
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities	97,847	226,680	102,800	233,373
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities	61,636	180,926	58,445	176,008

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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