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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 33,126	$ 24,238	$ 62,089	$ 48,831
Basic weighted average shares outstanding	36,876	36,699	36,826	36,703
Dilutive effect of stock options and restricted stock	872	943	884	931
Diluted weighted average shares outstanding	37,748	37,642	37,710	37,634
Basic earnings per share	$ 0.90	$ 0.66	$ 1.69	$ 1.33
Diluted earnings per share	$ 0.88	$ 0.64	$ 1.65	$ 1.30