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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income available to common shareholders	$ 28,782	$ 23,725	$ 56,732	$ 47,430
Denominator:
Basic weighted average shares outstanding	29,389,458	29,264,362	29,376,407	29,481,042
Effect of dilutive securities:
Diluted weighted average shares outstanding	29,550,418	29,477,870	29,555,985	29,694,081
Basic earnings per share	$ 0.98	$ 0.81	$ 1.93	$ 1.61
Diluted earnings per share	$ 0.97	$ 0.80	$ 1.92	$ 1.60
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities	98,813	136,872	99,699	142,460
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities	62,147	76,636	79,879	70,579

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

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