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Convertible Preferred Shares - Schedule of Convertible Preferred Shares Activities (Detail) ¥ in Thousands, $ in Thousands | 9 Months Ended
--- | ---
Sep. 30, 2020 CNY (¥) shares | Sep. 30, 2020 USD ($) shares | Sep. 30, 2019 CNY (¥) shares | Sep. 30, 2019 USD ($) shares
Temporary Equity [Line Items] |  |  |  |
Stock issued during period, value, new issues | ¥ | ¥ 697,878 |  |  |
Conversion to ordinary shares upon IPO, value | ¥ | 3,104,177 |  |  |
Series A Convertible Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Opening Balance | ¥ 687,482 | $ 102,852 | ¥ 687,482 | $ 102,852
Opening Balance, Shares | 30,227,056 | 30,227,056 | 30,227,056 | 30,227,056
Stock issued during period, value, new issues | $ |  |  |  |
Conversion to ordinary shares upon IPO, value | ¥ (687,482) | $ (102,852) |  |
Conversion to ordinary shares upon IPO, shares | (30,227,056) | (30,227,056) |  |
Closing Balance | ¥ 0 | $ 0 | ¥ 687,482 | $ 102,852
Closing Balance, Shares | 0 | 0 | 30,227,056 | 30,227,056
Series B Convertible Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Opening Balance | ¥ 921,243 | $ 139,407 | ¥ 921,243 | $ 139,407
Opening Balance, Shares | 30,305,212 | 30,305,212 | 30,305,212 | 30,305,212
Stock issued during period, value, new issues | $ |  |  |  |
Conversion to ordinary shares upon IPO, value | ¥ (921,243) | $ (139,407) |  |
Conversion to ordinary shares upon IPO, shares | (30,305,212) | (30,305,212) |  |
Closing Balance | ¥ 0 | $ 0 | ¥ 921,243 | $ 139,407
Closing Balance, Shares | 0 | 0 | 30,305,212 | 30,305,212
Series C Convertible Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Opening Balance | ¥ 1,306,633 | $ 197,478 | ¥ 1,306,633 | $ 197,478
Opening Balance, Shares | 31,046,360 | 31,046,360 | 31,046,360 | 31,046,360
Stock issued during period, value, new issues | $ |  |  |  |
Conversion to ordinary shares upon IPO, value | ¥ (1,306,633) | $ (197,478) |  |
Conversion to ordinary shares upon IPO, shares | (31,046,360) | (31,046,360) |  |
Closing Balance | ¥ 0 | $ 0 | ¥ 1,306,633 | $ 197,478
Closing Balance, Shares | 0 | 0 | 31,046,360 | 31,046,360
Series C-1 Convertible Preferred Stock [Member] |  |  |  |
Temporary Equity [Line Items] |  |  |  |
Opening Balance | ¥ 188,819 | $ 26,914 | ¥ 0 | $ 0
Opening Balance, Shares | 3,857,143 | 3,857,143 | 0 | 0
Stock issued during period, value, new issues | $ |  |  |  |
Conversion to ordinary shares upon IPO, value | ¥ (188,819) | $ (26,914) |  |
Conversion to ordinary shares upon IPO, shares | (3,857,143) | (3,857,143) |  |
Closing Balance | ¥ 0 | $ 0 | ¥ 0 | $ 0
Closing Balance, Shares | 0 | 0 | 0 | 0

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