Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share
Net income for basic and diluted earnings per share (in dollars)	$ 365,701	$ 367,779	$ 466,674	$ 411,090
Weighted-average common shares outstanding	219,744	217,940	219,450	217,797
Dilutive effect of stock options, performance share awards and restricted stock awards (in shares)	1,260	1,356	1,294	1,466
Diluted weighted-average shares outstanding	221,004	219,296	220,744	219,263
Basic earnings per share (in dollars per share)	$ 1.66	$ 1.69	$ 2.13	$ 1.89
Diluted earnings per share (in dollars per share)	$ 1.65	$ 1.68	$ 2.11	$ 1.87