Debt - 2011 Convertible Notes (Narrative) (Details) (Convertible Debt [Member], Unsecured Debt [Member], USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2013 2011 Senior Convertible Notes [Member]	Dec. 31, 2012 2011 Senior Convertible Notes [Member]	Sep. 30, 2013 2011 4.0% Notes [Member]
Debt Instrument [Line Items]
Unamortized debt discount and financing costs	$ 5.3	$ 9.3
Debt instrument, maturity date			Jun. 15, 2014
Principal amount	$ 202.3		$ 105.3