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Condensed Consolidating Financial Statements Condensed Consolidating Financial Statements (Details) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Jun. 30, 2012
Senior Notes [Member]
6% convertible senior notes [Domain]
Dec. 31, 2011
Senior Notes [Member]
6% convertible senior notes [Domain]
Feb. 23, 2010
Senior Notes [Member]
6% convertible senior notes [Domain]
Jun. 30, 2012
Senior Notes [Member]
Senior A Notes [Domain]
Dec. 31, 2011
Senior Notes [Member]
Senior A Notes [Domain]
Jul. 22, 2011
Senior Notes [Member]
Senior A Notes [Domain]
Jun. 30, 2012
Senior Notes [Member]
Senior B Notes [Domain]
Dec. 31, 2011
Senior Notes [Member]
Senior B Notes [Domain]
Jul. 22, 2011
Senior Notes [Member]
Senior B Notes [Domain]
Debt Instrument, Face Amount $ 1,388.3 $ 1,358.8 $ 69.4 $ 69.4 $ 70.0 $ 153.6 $ 146.3 $ 140.0 $ 94.3 $ 98.0 $ 100.0