Debt (Details 1) (Convertible subordinated notes [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Convertible subordinated notes [Member]
Total interest expenses recognized on the convertible subordinated notes
Coupon rate interest	$ 17.4	$ 17.4	$ 17.4
Amortized debt discount	11.3	10.5	9.6
Total interest expenses recognized on the convertible subordinated notes	$ 28.7	$ 27.9	$ 27.0