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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share Basic And Diluted [Abstract]
Net income	$ 24,238	$ 18,191	$ 48,831	$ 35,666
Basic weighted average shares outstanding	36,699	37,015	36,703	37,068
Dilutive effect of stock options and restricted stock	943	927	931	951
Diluted weighted average shares outstanding	37,642	37,942	37,634	38,019
Basic earnings per share	$ 0.66	$ 0.49	$ 1.33	$ 0.96
Diluted earnings per share	$ 0.64	$ 0.48	$ 1.30	$ 0.94