Merger Accounting - Schedule of Business Acquisitions by Acquisition, Contingent Consideration (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Mar. 13, 2019	Mar. 31, 2019
Acquisition Date [Line Items]
Fair value of consideration issued it effect the Merger		$ 45,541
Arsanis
Acquisition Date [Line Items]
Number of shares of the combined organization owned by Arsanis stockholders	2,440,582
Multiplied by the fair value per share of Arsanis common stock (usd per share)	$ 18.66
Fair value of consideration issued it effect the Merger	$ 45,541
Fair value of replacement awards held by former employees, board of directors and consultants of Arsanis that were vested as of the Merger.	817
Purchase price:	$ 46,358