Severance and Retention Costs, Akcea Acquisition (Details) - Akcea Acquisition [Member] $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)
Severance and Retention Costs [Abstract]
Total estimated expenses	$ 28.5	$ 28.5
Expenses incurred from inception to June 30, 2021	25.2	25.2
Remaining estimated expenses to be recognized through October 2021	3.3	3.3
Beginning balance		14.7
Amounts expensed during the period		11.2
Reserve adjustments during the period		(1.4)
Net amount expensed during the period	4.4	9.8
Amounts paid during the period		(18.1)
Ending balance	6.4	6.4
Research, Development and Patent Expenses [Member]
Severance and Retention Costs [Abstract]
Net amount expensed during the period	1.3	3.8
Selling, General and Administrative Expenses [Member]
Severance and Retention Costs [Abstract]
Net amount expensed during the period	$ 3.1	$ 6.0