Earnings Per Common Share Basic and Diluted (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator-basic and diluted
Net income	$ 10,309	$ 22,522	$ 55,704	$ 57,886
Denominator
Weighted average number of common shares outstanding-basic	41,094	39,789	40,771	39,637
Effect of dilutive stock options	426	414	418	353
Effect of dilutive restricted shares	462	616	493	618
Weighted average number of common shares outstanding-diluted	41,982	40,819	41,682	40,608
Earnings per common share-basic	$ 0.25	$ 0.57	$ 1.37	$ 1.46
Earnings per common share-diluted	$ 0.25	$ 0.55	$ 1.34	$ 1.43
Stock Options and Restricted Shares
Denominator
Anti-dilutive securities excluded from computation of earnings per share	1,360	2,741	1,685	3,185