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Net Loss Per Share - Additional Information (Detail) - shares |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Oct. 10, 2017 | Jul. 01, 2017 | Mar. 31, 2018 | Dec. 31, 2017
JGB Debt [Member] |  |  |  |
Schedule of Net Income (Loss) Per Share [Line Items] |  |  |  |
Shares issued upon conversion |  | 1,022,544 | 6,415,039 | 6,415,039
Underwritten Public Offering [Member] |  |  |  |
Schedule of Net Income (Loss) Per Share [Line Items] |  |  |  |
Common stock shares issued | 4,992,840 |  |  |

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