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Acquisitions (Details Textual) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Feb. 28, 2015 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Feb. 12, 2015
Business Acquisition [Line Items] |  |  |  |  |  |
Acquired in-process research and development |  |  | $ 120.0 | $ 0.0 | $ 0.0 |
Potential future milestone payments |  |  | 4,200.0 |  |  |
Goodwill |  |  | $ 4,632.5 | $ 3,669.3 | $ 2,663.8 |
Remedy Pharmaceutical [Member] |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Acquired in-process research and development |  | $ 120.0 |  |  |  |
Convergence Pharmaceuticals |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Cash portion of consideration | $ 200.1 |  |  |  |  |
Potential future milestone payments |  |  |  |  |  | $ 450.0
Contingent consideration obligation | $ 274.5 |  |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net |  |  |  |  |  | 474.6
In-process research and development |  |  |  |  |  | 424.6
Goodwill |  |  |  |  |  | 128.3
BIIB074 | Convergence Pharmaceuticals |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |
Potential future milestone payments |  |  |  |  |  | $ 350.0

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