License and Collaboration Agreements - Summary of Revenues by Collaboration and by Category of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	$ 77,517	$ 15,000	$ 8,353
Gilead License To Zimberelimab
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	55,096
Gilead Access Rights
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	15,421
Taiho License to Zimberelimab
License And Collaboration Agreements [Line Items]
Collaboration and license revenue		8,000
Taiho License to Etrumadenant
License And Collaboration Agreements [Line Items]
Collaboration and license revenue			3,000
Taiho Collaboration Agreement
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	$ 7,000	$ 7,000	$ 5,353