Loss on Sale of Nonfinancial Assets	9 Months Ended
Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Loss on Sale of Nonfinancial Assets	Loss on Transfer of Nonfinancial AssetsDuring the quarter ended September 30, 2019, the Company entered into contractual arrangements with two third parties that transferred the rights to develop and commercialize the programs underlying IPR&D intangible assets acquired in the merger with Arsanis. As of September 30, 2019, all programs underlying IPR&D intangible assets acquired in the Merger were transferred to these third parties and the Company has no continuing involvement in any ongoing research and development activities associated with the programs. The Company concluded that these third parties are "non-customers" as the underlying development programs transferred to these third parties are focused on potential drug candidates that were not aligned with the Company's strategic focus and, therefore, are not an output of the Company's ordinary activities. Accordingly, the Company accounted for these transactions under ASC Topic 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets ("ASC 610-20"). As a result of the transfer of control of the IPR&D projects to third parties, the Company derecognized the IPR&D intangible assets through a charge to "loss on transfer of non-financial assets" during the third quarter of 2019. The $4.0 million loss includes the carrying value of the IPR&D of $4.9 million, partially offset by $0.9 million of non-refundable, upfront fees received from the third parties. In accordance with the contractual arrangements with these third parties, the Company is entitled to future fees that are contingent on the success of the third parties in advancing the IPR&D project toward commercialization. These future fees, if any, will be recognized in future periods as gains on the transfer of non-financial assets in accordance with ASC 610-20, which generally provides that the fees would be recognized when it is probable that a future reversal of the fees that would be material to cumulative fees recognized to date would not occur.

Loss on Sale of Nonfinancial Assets

9 Months Ended

Sep. 30, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Loss on Transfer of Nonfinancial AssetsDuring the quarter ended September 30, 2019, the Company entered into contractual arrangements with two third parties that transferred the rights to develop and commercialize the programs underlying IPR&D intangible assets acquired in the merger with Arsanis. As of September 30, 2019, all programs underlying IPR&D intangible assets acquired in the Merger were transferred to these third parties and the Company has no continuing involvement in any ongoing research and development activities associated with the programs. The Company concluded that these third parties are "non-customers" as the underlying development programs transferred to these third parties are focused on potential drug candidates that were not aligned with the Company's strategic focus and, therefore, are not an output of the Company's ordinary activities. Accordingly, the Company accounted for these transactions under ASC Topic 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets ("ASC 610-20"). As a result of the transfer of control of the IPR&D projects to third parties, the Company derecognized the IPR&D intangible assets through a charge to "loss on transfer of non-financial assets" during the third quarter of 2019. The $4.0 million loss includes the carrying value of the IPR&D of $4.9 million, partially offset by $0.9 million of non-refundable, upfront fees received from the third parties. In accordance with the contractual arrangements with these third parties, the Company is entitled to future fees that are contingent on the success of the third parties in advancing the IPR&D project toward commercialization. These future fees, if any, will be recognized in future periods as gains on the transfer of non-financial assets in accordance with ASC 610-20, which generally provides that the fees would be recognized when it is probable that a future reversal of the fees that would be material to cumulative fees recognized to date would not occur.