Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, Antibody Collaboration (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	$ 401.1	$ (84.2)
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	172.8
Revenue recognized that was included in deferred revenue at the beginning of the period	$ (75.1)