Fair Value Measurements - Additional Information (Details) $ in Millions	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash	$ 2,200.0	$ 2,300.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining milestone payment	$ 678.3
Level 3 | Minimum | Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, measurement input (as a percent)	0.006
Level 3 | Maximum | Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, measurement input (as a percent)	0.019