Earnings per Share - Schedule of Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Basic earnings per share, Net Income	$ 97,950	$ 87,176	$ 60,161	$ 75,365
Diluted earnings per share, Net Income	$ 97,950	$ 87,176	$ 60,161	$ 75,365
Basic earnings per share, Shares	86,006	86,715	86,096	87,329
Effect of dilutive incentive-based awards, Shares	94	309	111	319
Diluted earnings per share, Shares	86,100	87,024	86,207	87,648
Basic earnings per share, Per Share Amount	$ 1.14	$ 1.01	$ 0.70	$ 0.86
Diluted earnings per share, Per Share Amount	$ 1.14	$ 1.00	$ 0.70	$ 0.86