Earnings Per Share (Narrative) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	2 Months Ended	12 Months Ended		26 Months Ended
	Feb. 28, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 28, 2013
Earnings Per Share
Common stock repurchased, shares	2,100	16,201	15,877	34,100
Common stock repurchased, average price per share	$ 90.09	$ 89.20	$ 61.49	$ 76.37
Common stock repurchased, value	$ 185,600	$ 1,445,044	$ 976,322	$ 2,600,000