Fair Value Of Financial Instruments (Schedule of Assets And Liabilities Measured At Fair Value On A Non-Recurring Basis) (Details) (Unsecured Debt [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
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
Carrying Amount [Member] | Senior Notes [Member] | 7.625% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior notes		150.0
Carrying Amount [Member] | Convertible Debt [Member] | 2009 Senior Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior convertible notes	12.6	12.7
Carrying Amount [Member] | Convertible Debt [Member] | 2011 Senior Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior convertible notes	198.3	193.0
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	380.0
Fair Value [Member] | Senior Notes [Member] | 7.625% Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior notes		154.9
Fair Value [Member] | Convertible Debt [Member] | 2009 Senior Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior convertible notes	26.6	21.0
Fair Value [Member] | Convertible Debt [Member] | 2011 Senior Convertible Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Non-Recurring Basis [Line Items]
Senior convertible notes	$ 428.3	$ 338.3