Collaborations - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended			12 Months Ended
	Dec. 18, 2019	Jan. 31, 2020	Dec. 31, 2018	Feb. 28, 2018	Dec. 31, 2020	Dec. 08, 2016
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue					$ 20,948
License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue					15,100
License \| Transfer of Exclusive License and Related Know-How
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue					15,000
Exclusive License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue					100
Collaboration
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue					5,848
Collaboration \| Reimbursable Out-of-Pocket and Personnel Costs Incurred Related to Research Services
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License and collaboration revenue					5,800
Pfizer Inc \| Collaboration Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment				$ 1,000	0
Pfizer Inc \| Collaboration Agreement \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Contingent cash payments upon achievement of certain clinical, regulatory and commercial milestones						$ 17,500
ISU Abxis \| Amended and Restated License Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Regulatory and development milestone payment			$ 2,500		0
ISU Abxis \| Amended and Restated License Agreement \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment			19,500		0
Commercial milestone payments			$ 17,000		$ 0
Biogen \| License and Collaboration Agreement (the “Biogen Agreement”)
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Research services	30 months
Research services option to extend	12 months
Biogen \| Exclusive License
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Up-front payments received		$ 15,000
Biogen \| Exclusive License \| Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Development and sales milestone payments		$ 340,000