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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 30,918	$ 22,715	$ 93,007	$ 71,546
Basic weighted average shares outstanding	36,889	36,681	36,847	36,695
Dilutive effect of stock options and restricted stock	903	962	891	941
Diluted weighted average shares outstanding	37,792	37,643	37,738	37,636
Basic earnings per share	$ 0.84	$ 0.62	$ 2.52	$ 1.95
Diluted earnings per share	$ 0.82	$ 0.60	$ 2.46	$ 1.90