Merger Accounting - Schedule of Business Acquisitions by Acquisition, Contingent Consideration (Footnote) (Detail)	Mar. 13, 2019 shares
Acquisition Date [Line Items]
Stock issued during period, shares, reverse stock splits	2,440,582
Arsanis
Acquisition Date [Line Items]
Stock issued during period, shares, reverse stock splits	14,643,737

Number of shares of equity interests issued or issuable to acquire entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration