Severance and Retention Costs, Akcea Acquisition (Details) - Akcea Acquisition [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Severance and Retention Costs [Abstract]
Total estimated expenses	$ 28.5
Remaining estimated expenses to be recognized through October 2021	7.8
Beginning balance	14.7
Amounts expensed during the period	6.1
Reserve adjustments during the period	(0.7)
Net amount expensed during the period	5.4	$ 15.3
Amounts paid during the period	(9.0)
Ending balance	11.1	$ 14.7
R&D Expenses [Member]
Severance and Retention Costs [Abstract]
Net amount expensed during the period	2.5
SG&A Expenses [Member]
Severance and Retention Costs [Abstract]
Net amount expensed during the period	$ 2.9