Balance Sheet Components - Intangible Assets, Net - Licenses (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)
Corporate Licensing Agreement
Intangible Assets, net
Maximum royalty base for royalty payments	$ 50,000,000
Patent License Agreement
Intangible Assets, net
Reimbursement of 3rd party costs (in percent)	0.33%
The University of Chicago Agreement | Patent License Agreement
Intangible Assets, net
Milestone payments under the agreement	$ 1,550,000
The Brigham and Women's Hospital, Inc | Patent License Agreement
Intangible Assets, net
Milestone payments under the agreement	860,000
The University of Iowa Research Foundation | Patent License Agreement
Intangible Assets, net
Milestone payments under the agreement	712,500
Brigham Young University | Patent License Agreement
Intangible Assets, net
Milestone payments under the agreement	400,000
National Institutes of Health | Patent License Agreement
Intangible Assets, net
Milestone payments under the agreement	850,000
Emergent Product Development Gaithersburg Inc | Corporate Licensing Agreement
Intangible Assets, net
Milestone payments under the agreement	$ 2,750,000