Collaboration Agreements - Summary of Total Consolidated Net Revenues from Strategic Collaborators (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	$ 60,209
Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	48,036
Balance without adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	94,978
Balance without adoption of ASC 606 | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	82,805	$ 122,512
Merck | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	36,608
Merck | Balance without adoption of ASC 606 | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	38,977	66,082
AstraZeneca | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	5,233
AstraZeneca | Balance without adoption of ASC 606 | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	37,235	45,993
Vertex | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	6,195
Vertex | Balance without adoption of ASC 606 | Collaboration Revenue by Strategic Collaborator
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total collaboration revenue	$ 6,593	$ 10,437