Earnings Per Common Share Basic and Diluted (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
Numerator — basic and diluted
Net income	$ 32,214	$ 21,691	$ 41,074	$ 78,419
Denominator
Weighted average number of common shares outstanding — basic	37,431	41,239	39,301	40,856
Effect of dilutive stock options	31	350	96	266
Effect of dilutive restricted shares	284	476	318	483
Weighted average number of common shares outstanding — diluted	37,746	42,065	39,715	41,605
Earnings per common share — basic	$ 0.86	$ 0.53	$ 1.05	$ 1.92
Earnings per common share — diluted	$ 0.85	$ 0.52	$ 1.03	$ 1.88
Stock Options And Restricted Shares
Denominator
Antidilutive stock options and restricted shares	2,328	753	1,755	1,595