Fair Value of Financial Instruments (Schedule Of Fair Values Of Financial Assets and Liabilities Measured On A Non-Recurring Basis) (Details) (Unsecured Debt [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Carrying Amount [Member] | Senior Notes [Member] | 4.875% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior notes	$ 400.0	$ 400.0
Carrying Amount [Member] | Convertible Debt [Member] | 2009 Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Convertible notes	12.6	12.6
Carrying Amount [Member] | Convertible Debt [Member] | 2011 Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Convertible notes	199.7	198.3
Fair Value [Member] | Senior Notes [Member] | 4.875% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior notes	390.5	380.0
Fair Value [Member] | Convertible Debt [Member] | 2009 Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Convertible notes	35.0	26.6
Fair Value [Member] | Convertible Debt [Member] | 2011 Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Convertible notes	$ 563.2	$ 428.3