Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, Antibody Collaboration (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	$ 426.5	$ (54.5)
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	86.0
Revenue recognized that was included in deferred revenue at the beginning of the period	$ (20.1)