Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, Antibody Collaboration (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Increase due to shipments of commercial supplies to Sanofi	$ 375.8	$ (29.5)
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Increase due to shipments of commercial supplies to Sanofi	294.3
Revenue recognized that was included in deferred revenue at the beginning of the period	$ (159.0)