Collaboration and License Agreements - Sanofi, Immuno-Oncology Narrative (Details) - Sanofi Collaboration Agreement, Immuno-oncology - USD ($)		1 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Aug. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015
Disaggregation of Revenue [Line Items]
Excess share of profit not required to to be applied to reimburse development cost						10.00%
Contingent reimbursement obligation				$ 75,000,000
Maximum shares the collaborator could sell (in shares)				1,400,000
Number of shares the collaborator available to sell (in shares)				869,828
Amount related to obligation to pay gross profits sharing				$ 78,200,000
Upfront payment made			$ 20,000,000.0
Remaining performance obligation				1,138,000,000
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
License agreement term						5 years
Additional years to extend the agreement						3 years
Amended IO Discovery Agreement
Disaggregation of Revenue [Line Items]
Increase as a result of payment received from Sanofi in connection with the termination of the 2015 IO Discovery Agreement				$ 415,900,000	$ 135,000,000.0
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
Potential maximum expenditure	70,000,000.0				$ 70,000,000.0
Optional payment to increase development cost funding	$ 20,000,000.0
IO Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received						$ 640,000,000.0
IO License and Collaboration Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received						$ 375,000,000.0
Excess share of profit not required to to be applied to reimburse development cost						10.00%
Maximum amount of sales milestone payments if total sales achieve specific levels		$ 375,000,000.0
Period of notice to opt out of further development and or commercialization				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
Through December 31, 2023 | Libtayo
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid			8.00%
January 1, 2024 Through December 31, 2026 | Libtayo
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid			2.50%