Stockholders' Equity (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended		30 Months Ended
	Jun. 30, 2004	Mar. 31, 2013 employee_groups	Mar. 31, 2012	Jan. 01, 2007	Dec. 31, 2012	Mar. 31, 2013 2011 Stock Plan [Member]	Apr. 26, 2013 Subsequent Event [Member]
Components of Stockholders' Equity [Line Items]
Common stock, shares issued		56,143,986			55,587,167		2,300,000
Shares reserved for future issuance						3,800,000
Total intrinsic value of options exercised		$ 50.0	$ 11.7
Cash received from option exercised		39.1	1.2
Exercise period after employment termination	3 months			1 year
Full exercise period		10 years
Number of employee groups		2
Weighted-average fair value of employee stock options granted per share		$ 72.71	$ 55.65
Stock-based compensation expense		17.7	19.3
Income tax benefit		$ 6.8	$ 6.7