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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 38,023	$ 33,126	$ 80,486	$ 62,089
Basic weighted average shares outstanding	36,853	36,876	36,852	36,826
Dilutive effect of stock options and restricted stock	1,224	872	1,243	884
Diluted weighted average shares outstanding	38,077	37,748	38,095	37,710
Basic earnings per share	$ 1.03	$ 0.90	$ 2.18	$ 1.69
Diluted earnings per share	$ 1.00	$ 0.88	$ 2.11	$ 1.65