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Income Taxes (Details Textual) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax assets, net | $ 500.0 |  | $ 500.0 |  |
Deferred tax assets, gross | 875.0 |  | 875.0 |  |
Deferred tax assets, unrecognized tax benefit | 375.0 |  | 375.0 |  |
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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