Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net income	$ 8,086	$ 3,744	$ 18,715	$ 17,553	$ 5,153	$ 8,913	$ 15,161	$ 12,295	$ 48,098	$ 41,521	$ 34,598
Denominator:
Basic weighted average shares outstanding	30,766,943	31,227,643	31,735,333	31,683,672	31,641,963	31,606,264	32,898,288	33,128,676	31,350,542	32,319,649	33,589,682
Effect of dilutive securities:
Diluted weighted average shares outstanding	30,966,682	31,537,010	32,142,939	32,094,828	32,085,210	32,008,781	33,307,463	33,599,438	31,682,509	32,751,074	34,273,502
Basic earnings per share	$ 0.26	$ 0.12	$ 0.59	$ 0.55	$ 0.16	$ 0.28	$ 0.46	$ 0.37	$ 1.53	$ 1.28	$ 1.03
Diluted earnings per share	$ 0.26	$ 0.12	$ 0.58	$ 0.55	$ 0.16	$ 0.28	$ 0.46	$ 0.37	$ 1.52	$ 1.27	$ 1.01
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities									197,299	262,730	510,706
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities									134,668	168,695	173,114