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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 34,130	$ 30,918	$ 114,616	$ 93,007
Basic weighted average shares outstanding	36,865	36,889	36,856	36,847
Dilutive effect of stock options and restricted stock	1,154	903	1,213	891
Diluted weighted average shares outstanding	38,019	37,792	38,069	37,738
Basic earnings per share	$ 0.93	$ 0.84	$ 3.11	$ 2.52
Diluted earnings per share	$ 0.90	$ 0.82	$ 3.01	$ 2.46