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Commitments and Contingences (Details) - Fumapharm AG - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2015 | Dec. 31, 2006 | Jun. 30, 2013
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cash portion of consideration |  | $ 220.0 |
TECFIDERA |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Maximum contingent consideration in the form of development and approval milestones |  |  | $ 15.0
Four billion |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cash portion of consideration | $ 550.0 |  |
Cumulative sales level | 4,000.0 |  |
Five billion |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cumulative sales level | 5,000.0 |  |
Six billion |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cash portion of consideration | 300.0 |  |
Cumulative sales level | 6,000.0 |  |
Each additional one billion up to twenty billion |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cumulative sales level | 20,000.0 |  |
One billion |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cumulative sales level | 1,000.0 |  |
Three billion |  |  |
Business Acquisition, Contingent Consideration [Line Items] |  |  |
Cumulative sales level | $ 3,000.0 |  |

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