Earnings Per Share - Schedule of Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Basic earnings per share, Net Income	$ 87,176	$ 120,740	$ 75,365	$ 64,889
Diluted earnings per share, Net Income	$ 87,176	$ 120,740	$ 75,365	$ 64,889
Basic earnings per share, Shares	86,715	89,610	87,329	86,867
Effect of dilutive incentive-based awards, Shares	309	596	319	664
Diluted earnings per share, Shares	87,024	90,206	87,648	87,531
Basic earnings per share, Per Share Amount	$ 1.01	$ 1.35	$ 0.86	$ 0.75
Diluted earnings per share, Per Share Amount	$ 1.00	$ 1.34	$ 0.86	$ 0.74