Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income available to common shareholders	$ 3,744	$ 8,913	$ 40,012	$ 36,368
Denominator:
Basic weighted average shares outstanding	31,227,643	31,606,264	31,547,212	32,538,832
Effect of dilutive securities:
Diluted weighted average shares outstanding	31,537,010	32,008,781	31,923,255	32,966,317
Basic earnings per share	$ 0.12	$ 0.28	$ 1.27	$ 1.12
Diluted earnings per share	$ 0.12	$ 0.28	$ 1.25	$ 1.10
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities	182,082	237,602	216,276	268,016
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities	127,285	164,915	159,767	159,469