Collaboration Agreements - Timing of Differences (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jun. 30, 2019	Jan. 01, 2019
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price	$ 249.5
PCVSAV Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price			$ 213.0
PCVSAV Agreement | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price	83.8
Combined 2018 AZ Agreements
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price			400.0
Combined 2018 AZ Agreements | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price	100.7
Combined 2018 AZ Agreements | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price	110.4
VEGF Exercise 2016
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price			55.1
VEGF Exercise 2016 | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price	53.7
Vertex Agreement
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price		$ 4.1	$ 24.4
Vertex Agreement | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price	$ 1.6