Earnings Per Share - Computation of Basic and Diluted Earnings Per Common Share (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
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 22,715	$ 17,504	$ 71,546	$ 53,170
Basic weighted average shares outstanding	36,681	36,856	36,695	36,997
Dilutive effect of stock options and restricted stock	962	949	941	950
Diluted weighted average shares outstanding	37,643	37,805	37,636	37,947
Basic earnings per share	$ 0.62	$ 0.47	$ 1.95	$ 1.44
Diluted earnings per share	$ 0.60	$ 0.46	$ 1.90	$ 1.40