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Income Taxes (Details Textual) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2022 | Jun. 30, 2021
Income Tax Contingency [Line Items] |  |  |  |  |  |
Deferred tax assets, net | $ 500.0 |  | $ 500.0 |  |  |
Deferred tax assets, gross |  |  |  |  |  | $ 875.0
Deferred tax assets, unrecognized tax benefit |  |  |  |  |  | $ 375.0
Forecast |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Decrease in unrecognized tax benefits is reasonably possible |  |  |  |  | $ 20.0 |
TECFIDERA |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Deferred tax assets, decrease in value | 1,700.0 |  | 1,700.0 |  |  |
Deferred tax liabilities, decrease in value | 1,600.0 |  | 1,600.0 |  |  |
Deferred tax asset, increase (decrease) in value | $ 92.6 |  | $ 92.6 |  |  |
Deferred tax liabilities, increase (decrease) in value |  | $ 88.7 |  | $ 88.7 |  |

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