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Merger Accounting - Schedule of Business Acquisitions by Acquisition, Contingent Consideration (Detail) $ / shares in Units, $ in Thousands | 3 Months Ended
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Mar. 31, 2019 USD ($) $ / shares shares
Acquisition Date [Line Items] |  |
Fair value of consideration issued it effect the Merger | $ 45,541 |
Arsanis [Member] |  |
Acquisition Date [Line Items] |  |
Number of shares of the combined organization owned by Arsanis stockholders | shares | 2,440,582 | [1]
Multiplied by the fair value per share of Arsanis common stock | $ / shares | $ 18.66 | [2]
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 |
[1] | The number of shares of 2,440,582 represents the historical 14,643,737 shares of Arsanis common stock outstanding immediately prior to the closing of the Merger, adjusted for the Reverse Stock Split.
[2] | Based on the last reported sale price of Arsanis common stock on the Nasdaq Global Market on March 13, 2019, the closing date of the Merger, and gives effect to the Reverse Stock Split.

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