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