Balance Sheet Components - Intangible Assets, Net - Licenses (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
The University of Chicago Agreement
Intangible Assets, net
Maximum contingent milestone payments	$ 1,600,000
Milestone payments accrued	0	$ 0
The Brigham and Women's Hospital, Inc
Intangible Assets, net
Maximum contingent milestone payments	860,000
Milestone payments accrued	0	0
The University of Iowa Research Foundation
Intangible Assets, net
Maximum contingent milestone payments	712,500
Milestone payments accrued	0	0
Brigham Young University
Intangible Assets, net
Maximum contingent milestone payments	400,000
Milestone payments accrued	$ 0	0
Reimbursement of 3rd party costs (in percent)	0.33%
National Institutes of Health
Intangible Assets, net
Maximum contingent milestone payments	$ 850,000
Milestone payments accrued	0	0
Kenta Biotech Ltd
Intangible Assets, net
Accrued royalty obligation	488,000	$ 0
Maximum royalty base for royalty payments	50,000,000
Emergent Product Development Gaithersburg Inc
Intangible Assets, net
Milestone payments under the agreement	$ 2,800,000