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Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands |  |  |  | 3 Months Ended | 12 Months Ended
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Nov. 14, 2017 USD ($) $ / shares shares | Nov. 06, 2017 USD ($) $ / shares shares | Oct. 20, 2017 | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) $ / shares | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) $ / shares | Dec. 31, 2015 USD ($)
Nature Of Business And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Entity incorporation month and year |  |  |  |  |  |  |  |  |  |  |  | 2013-12 |  |
State of incorporation |  |  |  |  |  |  |  |  |  |  |  | Delaware |  |
Merger date |  |  |  |  |  |  |  |  |  |  |  | Jun. 30, 2017 |  |
Business combination exchange ratio |  |  |  |  |  |  |  |  |  |  |  | 1 |  |
Share price | $ / shares |  |  |  |  |  |  |  | $ 0.001 |  |  |  |  | $ 0.001 |
Net proceeds from issuance of common stock |  |  |  |  |  |  |  |  |  |  |  | $ 77,749 |  |
Net loss |  |  |  | $ (13,862) | $ (9,836) | $ (9,169) | $ (5,876) | $ (7,211) | $ (6,316) | $ (6,059) | $ (5,905) | (38,743) | $ (25,491) | $ (10,154)
Accumulated deficit |  |  |  | $ (96,840) |  |  |  | $ (45,440) |  |  |  | $ (96,840) | $ (45,440) |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nature Of Business And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse stock split ratio |  |  | 0.164544 |  |  |  |  |  |  |  |  |  |  |
Reverse stock split |  |  | one-for-6.0774 |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Initial Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nature Of Business And Basis Of Presentation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of stock, shares | shares | 471,498 | 5,500,000 |  |  |  |  |  |  |  |  |  | 5,971,498 |  |
Share price | $ / shares | $ 14.00 | $ 14.00 |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock | $ 6,100 | $ 71,600 |  |  |  |  |  |  |  |  |  |  |  |

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