Fair Value Measurements (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Fair value of contingent consideration obligations
Fair value as of beginning of period	$ 81.2	$ 0
Acquisition date fair value of contingent consideration obligations related to acquisitions	38.8	81.2
Changes in the fair value of contingent consideration obligations	36.0
Payments of contingent consideration obligations	(5.0)
Fair value as of end of period	$ 151.0	$ 81.2

Fair value, as of the acquisition date, of potential payments under the contingent consideration arrangement including cash and shares.

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+ Details