Earnings Per Share (Details) (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]
Net income for basic and diluted earnings per share (in dollars)	$ 490,248	$ 365,701	$ 654,378	$ 466,674
Weighted-average common shares outstanding	222,523	219,744	222,007	219,450
Dilutive effect of stock options, performance share awards and restricted stock awards (in shares)	1,336	1,260	1,344	1,294
Diluted weighted-average shares outstanding	223,859	221,004	223,351	220,744
Basic earnings per share (in dollars per share)	$ 2.20	$ 1.66	$ 2.95	$ 2.13
Diluted earnings per share (in dollars per share)	$ 2.19	$ 1.65	$ 2.93	$ 2.11