Stockholders' Equity (Share Repurchase Programs) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stockholders' Equity Note [Abstract]
Shares of common stock repurchased	396,523	690,052	1,370,619	1,211,052
Value of common stock repurchased	$ 21.9	$ 31.0	$ 70.8	$ 52.0