Collaborations - Additional Information (Detail) - USD ($)	1 Months Ended		9 Months Ended
	Dec. 31, 2018	Feb. 28, 2018	Sep. 30, 2019	Dec. 08, 2016
Pfizer Inc | Collaboration Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment		$ 1,000,000	$ 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				$ 17,500,000
ISU Abxis | Amended and Restated License Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Regulatory and development milestone payment	$ 2,500,000
ISU Abxis | Amended and Restated License Agreement | Maximum
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Milestone payment	19,500,000
Commercial milestone payments	$ 17,000,000