Collaboration and Other Agreements - NIAID Contract (Details)		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 15, 2015 USD ($) Molecule	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Collaboration And Other Agreements [Line Items]
Revenues		$ 20,798,000	$ 1,663,000	$ 44,327,000	$ 5,383,000
NIAID
Collaboration And Other Agreements [Line Items]
Commercialization of molecules | Molecule	2
Base period	$ 7,500,000
Additional development funding options under agreement	17,000,000.0
Total potential value	$ 24,500,000
Proceeds from additional development funding options under agreement						$ 10,800,000
Revenues From Grants | NIAID
Collaboration And Other Agreements [Line Items]
Revenues		$ 200,000	$ 400,000	$ 600,000	$ 1,500,000