Earnings Per Share (Narrative) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended		31 Months Ended
	Aug. 08, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Aug. 08, 2013
Earnings Per Share
Shares repurchased	500	2,546	4,518	5,013	6,288	37,600
Average price per share	$ 113.66	$ 107.61	$ 97.47	$ 100.10	$ 94.52	$ 79.27
Total investment	$ 56,300	$ 273,946	$ 440,369	$ 501,838	$ 594,355	$ 2,980,000