Nature of the Business and Basis of Presentation (Details)			12 Months Ended
	Mar. 18, 2019	Mar. 13, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Percentage of voting interest			64.00%
Stock split, conversion ratio		0.1667
Proceeds from sale of common stock and warrants, net of issuance costs			$ 139,388,000	$ 0	$ 0
Proceeds from borrowings under loan and security agreements, net of issuance costs			9,849,000	$ 9,908,000	$ 6,000,000
Arsanis
Restructuring Cost and Reserve [Line Items]
Exchange ratio		0.5702
Cash, cash equivalents and restricted cash		$ 26,406,000	26,400,000
Hercules Loan Agreements
Restructuring Cost and Reserve [Line Items]
Proceeds from borrowings under loan and security agreements, net of issuance costs			$ 9,800,000
Hercules Loan Agreements | Arsanis
Restructuring Cost and Reserve [Line Items]
Exchange ratio	0.5702
Hercules Amended and Restated Loan Agreement | Additional Term Loan One
Restructuring Cost and Reserve [Line Items]
Additional borrowing capacity						$ 5,000,000.0
Hercules Amended and Restated Loan Agreement | Additional Term Loan Two
Restructuring Cost and Reserve [Line Items]
Additional borrowing capacity						$ 10,000,000.0