Fair Value Measurement (Liabilities Narrative) (Details 3) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Measurement Liabilities Narrative Details 3
Brigham Women's Hospital royalty liability, fair value	$ 5.0	$ 4.8
Brigham Women's Hospital royalty liability, carrying value	$ 6.6	$ 6.6

Carrying value as of the balance sheet date of obligations incurred through that date and payable for royalties.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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