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Fair Value Measurements (Debt) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Fair Value    
Credit facility term loan $ 85.0  
Credit facility term loan, non-current   85.0
Credit facility term loan, fair value 72.8 85.6
Convertible senior notes 530.0 575.0
Convertible senior notes, fair value $ 246.1 $ 517.9