Fair Value of Financial Instruments (Schedule of Fair Value of Financial Instruments, Non-Recurring Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2014	Dec. 31, 2013
Senior Notes [Member] | 4.875% Senior Notes [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Debt instrument, interest rate (percentage)	4.875%
Fair Value Measurements, Non-Recurring [Member] | 2009 Convertible Notes [Member] | Carrying Amount [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Convertible notes	$ 0.0	$ 12.6
Fair Value Measurements, Non-Recurring [Member] | 2009 Convertible Notes [Member] | Fair Value [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Convertible notes	0.0	26.6
Fair Value Measurements, Non-Recurring [Member] | 2011 Convertible Notes [Member] | Carrying Amount [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Convertible notes	0.0	198.3
Fair Value Measurements, Non-Recurring [Member] | 2011 Convertible Notes [Member] | Fair Value [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Convertible notes	0.0	428.3
Fair Value Measurements, Non-Recurring [Member] | Senior Notes [Member] | 4.875% Senior Notes [Member] | Carrying Amount [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Senior notes	400.0	400.0
Fair Value Measurements, Non-Recurring [Member] | Senior Notes [Member] | 4.875% Senior Notes [Member] | Fair Value [Member]
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Senior notes	$ 375.0	$ 380.0