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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income	$ 12,629	$ 7,787	$ 23,725	$ 23,706	$ 8,086	$ 3,744	$ 18,715	$ 17,553	$ 67,847	$ 48,098	$ 41,521
Denominator:
Basic weighted average shares outstanding	29,318,915	29,295,284	29,264,362	29,697,722	30,766,943	31,227,643	31,735,333	31,683,672	29,394,559	31,350,542	32,319,649
Effect of dilutive securities:
Diluted weighted average shares outstanding	29,543,842	29,516,718	29,477,870	29,910,292	30,966,682	31,537,010	32,142,939	32,094,828	29,612,669	31,682,509	32,751,074
Basic earnings per share	$ 0.43	$ 0.27	$ 0.81	$ 0.80	$ 0.26	$ 0.12	$ 0.59	$ 0.55	$ 2.31	$ 1.53	$ 1.28
Diluted earnings per share	$ 0.43	$ 0.26	$ 0.80	$ 0.79	$ 0.26	$ 0.12	$ 0.58	$ 0.55	$ 2.29	$ 1.52	$ 1.27
Stock Appreciation Rights and Options [Member]
Effect of dilutive securities:
Dilutive securities									125,119	197,299	262,730
Restricted Stock [Member]
Effect of dilutive securities:
Dilutive securities									92,991	134,668	168,695