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Subsequent Events - Additional Information (Detail) - American Depositary Shares - USD ($) $ / shares in Units, $ in Millions | Jul. 29, 2019 | Jul. 18, 2019 | Nov. 29, 2018 | Feb. 01, 2018
--- | --- | --- | --- | ---
Subsequent Event [Line Items] |  |  |  |
Issuance of stock (shares) |  |  | 11,111,112 | 19,178,082
Sale of stock price per share |  |  | $ 17.575 | $ 3.41
Over allotment option, exercisable period |  |  |  | 30 days
Over-Allotment Option |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Issuance of stock (shares) |  |  |  | 2,876,712
Subsequent Event |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Issuance of stock (shares) |  | 22,222,223 |  |
Sale of stock price per share |  | $ 18.00 |  |
Over allotment option, exercisable period |  | 30 days |  |
Subsequent Event | Over-Allotment Option |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Issuance of stock (shares) |  | 3,333,333 |  |
Sale of stock price per share |  | $ 18.00 |  |
Gross proceeds from public offering including exercised option | $ 460.0 |  |  |
Net proceeds from public offering including exercised option | $ 439.5 |  |  |

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