Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income	$ 5,153	$ 8,913	$ 15,161	$ 12,295	$ 15,103	$ (15,298)	$ 13,224	$ 21,569	$ 41,521	$ 34,598	$ 2,720
Denominator:
Basic weighted average shares outstanding									32,319,649	33,589,682	32,247,184
Effect of dilutive securities:
SARS and options									262,730	510,706	812,964
Restricted stock									168,695	173,114	103,598
Convertible notes											965,966
Diluted weighted average shares outstanding									32,751,074	34,273,502	34,129,712
Basic earnings per share	$ 0.16	$ 0.28	$ 0.46	$ 0.37	$ 0.46	$ (0.45)	$ 0.39	$ 0.64	$ 1.28	$ 1.03	$ 0.08
Diluted earnings per share	$ 0.16	$ 0.28	$ 0.46	$ 0.37	$ 0.45	$ (0.45)	$ 0.38	$ 0.62	$ 1.27	$ 1.01	$ 0.08