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Equity - Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |  |  | 6 Months Ended
--- | --- | --- | ---
Mar. 05, 2018 | Feb. 01, 2018 | Jun. 30, 2018
Stockholders Equity Note [Line Items] |  |  |
Net proceeds from public offering |  |  | $ 70,007
American Depositary Shares |  |  |
Stockholders Equity Note [Line Items] |  |  |
Issuance of stock (shares) |  | 19,178,082 |
Over allotment option, exercisable period |  | 30 days |
Sale of stock price per share |  | $ 3.41 |
Net proceeds from public offering |  | $ 70,000 |
American Depositary Shares | Over-Allotment Option |  |  |
Stockholders Equity Note [Line Items] |  |  |
Issuance of stock (shares) |  | 2,876,712 |
Issuance of stock (shares), exercised | 1,438,356 |  |

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