Stockholders' Equity Matters (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	0 Months Ended	1 Months Ended												3 Months Ended
	Nov. 21, 2012	Apr. 30, 2013	Mar. 31, 2013	Jan. 31, 2013	Dec. 31, 2012	Nov. 30, 2012	Nov. 21, 2012	Oct. 31, 2012	Sep. 30, 2012	Jul. 31, 2012	Jun. 30, 2012	Apr. 30, 2012	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Stockholders' Equity Note
Share repurchases authorized amount														$ 1,200,000
Remaining amount available under share repurchase program														66,035
Percentage of outstanding common stock authorized for repurchase														1.00%
Dividends declared (in dollars per share)			$ 0.2700		$ 0.2700			$ 4.0600	$ 0.2700		$ 0.2700		$ 0.2500	$ 0.2700	$ 0.2500
Dividends declared			51,460		51,296			700,000	46,473		46,336		42,791	52,448	42,791
Dividends paid ( in dollars per share)		$ 0.2700		$ 0.2700		$ 4.0600		$ 0.2700		$ 0.2700		$ 0.2500
Dividends paid							140,000							51,662	43,180
Number of trading days used for value of special dividend						3 days
Common stock value for special dividend (in dollars per share)	$ 32.87						$ 32.87
Common stock issued in special dividend	$ 560,000
Common stock issued in special dividend (in shares)	17,000