Collaboration, License, and Other Agreements - Sanofi, Immuno-Oncology Narrative (Details) - Sanofi Collaboration Agreement, Immuno-oncology - USD ($)		1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Aug. 31, 2018	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2015
Disaggregation of Revenue [Line Items]
Percentage of quarterly profits require to be paid for reimbursement of development costs					10.00%
Contingent reimbursement obligation					$ 107,000,000
Upfront payment made			$ 20,000,000.0
Remaining performance obligation					557,500,000
Libtayo | Through December 31, 2023
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid			8.00%
Libtayo | January 1, 2024 Through December 31, 2026
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid			2.50%
IO Discovery Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received							$ 265,000,000.0
Potential future R&D expenses							1,090,000,000.000
Maximum funding amount of research activities to be reimbursed per agreement							825,000,000.0
BCMAxCD3 Program
Disaggregation of Revenue [Line Items]
Aggregate payment received with regards to amendment				$ 461,900,000
Expenditure costs cap	$ 70,000,000.0
MUC16xCD3 Program
Disaggregation of Revenue [Line Items]
Expenditure costs cap	$ 50,000,000.0
IO License and Collaboration Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received							375,000,000.0
Maximum amount of sales milestone payments if total sales achieve specific levels					375,000,000.0
Period for achieving sales target for milestone payment, rolling basis		12 months
IO License and Collaboration Agreement | PD-1
Disaggregation of Revenue [Line Items]
Levels of twelve month sales at which sales milestone payments would be received		$ 2,000,000,000.0
IO Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received							$ 640,000,000.0
Amended IO Discovery Agreement | Other Operating Income (Expense)
Disaggregation of Revenue [Line Items]
Cumulative catch-up adjustment to revenue, modification of contract					$ 135,400,000	$ 135,000,000.0