Stockholders' Equity (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Apr. 26, 2012	Mar. 31, 2013	Mar. 31, 2012	Jan. 16, 2013
Stockholders' Equity Note [Abstract]
Increase in stock repurchase authorized amount	$ 150.0
Stock Repurchase Program, Number of Shares Authorized to be Repurchased				150.0
Shares repurchased during period (shares)		1.1	0.2
Value of shares repurchased during period		40.3	7.9
Remaining amount available for future purchases of shares under approved repurchase program		119.3
Additional stock-based compensation		$ 1.9	$ 1.8