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Agreements - Amgen/Oxford BioTherapeutics (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2000 USD ($) item	Oct. 31, 2013 USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer	$ 132,299	$ 82,271	$ 53,446
Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Revenue from contract with customer	4,000
Number of single-target licenses \| item				4
Number of licenses terminated \| item				4
Amgen/Oxford BioTherapeutics \| Development and regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment					$ 29,000
Amgen/Oxford BioTherapeutics \| Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment	3,000
Amgen/Oxford BioTherapeutics \| Milestone payments
Collaborative Agreements disclosures
Potential milestone payment					5,000
Upfront payment \| Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Revenue from contract with customer				$ 1,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer	$ 63,742	$ 34,788	$ 15,280
License and milestone fees \| Amgen/Oxford BioTherapeutics
Collaborative Agreements disclosures
Potential milestone payment					$ 34,000