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Income Taxes (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Statutory rate	21.00%	21.00%	21.00%	21.00%
State taxes	1.30%	0.40%	1.10%	0.50%
Taxes on foreign earnings	(7.70%)	(3.40%)	(9.10%)	(3.70%)
Credits and net operating loss utilization	(2.90%)	(1.00%)	(3.30%)	(1.00%)
Purchased intangible assets	(0.80%)	0.20%	(0.10%)	0.20%
TECFIDERA impairment	0.00%	2.70%	0.00%	1.50%
GILTI	1.50%	1.50%	1.30%	1.10%
Neurimmune tax impacts	(0.831)	(0.002)	(0.463)	(0.002)
Other	0.40%	0.70%	0.60%	0.40%
Effective tax rate	(70.30%)	21.90%	(34.80%)	19.80%

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Effective Tax Rate Reconciliation, GILTI tax

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to depreciation and amortization.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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