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Ordinary Shares - Additional Information (Detail) $ / shares in Units, ¥ in Thousands |  |  |  | 9 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |
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Feb. 10, 2020 CNY (¥) shares | Feb. 10, 2020 USD ($) $ / shares shares | Jan. 31, 2020 USD ($) shares | Jan. 31, 2020 USD ($) shares | Jan. 17, 2020 $ / shares shares | Sep. 30, 2020 CNY (¥) shares | Sep. 30, 2020 USD ($) shares | Dec. 31, 2020 USD ($) shares | Sep. 30, 2020 USD ($) $ / shares shares | Jul. 15, 2020 CNY (¥) | Jul. 15, 2020 USD ($) | Dec. 31, 2019 $ / shares shares | Oct. 29, 2019 USD ($) $ / shares shares | Sep. 30, 2019 shares | Dec. 31, 2018 $ / shares shares | Dec. 31, 2017 $ / shares | Oct. 31, 2016 $ / shares
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ordinary shares, shares authorized |  |  |  |  |  | 800,000,000 |  |  | 800,000,000 |  |  | 500,000,000 |  |  |  |  |
Voting rights |  |  |  |  |  | Each ordinary share is entitled to one vote. | Each ordinary share is entitled to one vote. |  |  |  |  |  |  |  |  |  |
Ordinary shares, par value | $ / shares |  |  |  |  |  |  |  |  | $ 0.0001 |  |  | $ 0.0001 |  |  | $ 0.0001 | $ 0.0001 |
Proceeds from initial public offering |  |  |  |  |  | ¥ 726,300 | $ 106,972,000 |  |  |  |  |  |  |  |  |  |
Share price | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.77
American depository shares, common share equivalent | 23 | 23 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Prepaid Expensestock repurchase program |  |  |  |  |  | 34,051 |  |  | $ 5,015,000 |  |  |  |  |  |  |  |
Issuance of Private Placement |  |  |  |  |  | ¥ 1,980,548 | 291,703,000 |  |  |  |  |  |  |  |  |  |
2017 Employee Stock Option Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares Held in Employee Stock Option Plan |  |  |  |  |  | 115,888 |  |  | 115,888 |  |  |  |  |  |  |  |
Collaboration Agreement with Everest [Member] | Everest Member [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued upon conversion |  |  | 6,078,571 | 6,078,571 | 6,078,571 |  |  |  |  |  |  |  |  |  |  |  |
Hillhouse Entities [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Warrants | $ |  |  |  |  |  |  | 45.00 |  |  |  |  |  |  |  |  |  |
Hillhouse Entities [Member] | First Closing Period [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares, Issued |  |  |  |  |  | 20,421,378 |  |  | 20,421,378 |  |  |  |  |  |  |  |
Number of warrants issued |  |  |  |  |  | 3,744,032 |  |  | 3,744,032 |  |  |  |  |  |  |  |
Gross proceeds of shares and warrants | $ |  |  |  |  |  |  | 293,000,000 |  |  |  |  |  |  |  |  |  |
Hillhouse Entities [Member] | Second Closing Period [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares, Issued |  |  |  |  |  |  |  | 8,712,124 |  |  |  |  |  |  |  |  |
Number of warrants issued |  |  |  |  |  |  |  | 1,597,235 |  |  |  |  |  |  |  |  |
Gross proceeds of shares and warrants | $ |  |  |  |  |  |  |  | $ 125,000,000.0 |  |  |  |  |  |  |  |  |
Collaboration Agreement With Investores [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of Private Placement | $ |  |  |  |  |  |  | $ 418,000,000 |  |  |  |  |  |  |  |  |  |
American Depositary Shares [Member] | Investor Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of share issued, ADS |  |  |  |  |  | 5,341,267 | 5,341,267 |  |  |  |  |  |  |  |  |  |
Share price | $ / shares |  |  |  |  |  |  |  |  | $ 45 |  |  |  |  |  |  |  |
Proceeds from Issuance of Warrants | $ |  |  |  |  |  |  | $ 104,500,000 |  |  |  |  |  |  |  |  |  |
American Depositary Shares [Member] | IPO [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of share issued, ADS |  |  | 7,407,400 | 7,407,400 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of share issued, price per share | $ / shares |  |  |  |  | $ 14.00 |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from initial public offering | $ |  |  | $ 103,700,000 | $ 103,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |
American Depositary Shares [Member] | Over-Allotment Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of share issued, ADS | 8,175,750 | 8,175,750 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from initial public offering, net | ¥ 697,788 | $ 101,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from initial public offering | $ |  | $ 114,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock Shares Issuable |  | 768,350 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price | $ / shares |  | $ 14.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
American Depositary Shares [Member] | Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of share issued, ADS |  |  |  |  |  | 29,133,502 | 29,133,502 |  |  |  |  |  |  |  |  |  |
Share price | $ / shares |  |  |  |  |  |  |  |  | $ 33 |  |  |  |  |  |  |  |
Issuance of Private Placement | $ |  |  |  |  |  |  | $ 418,000,000 |  |  |  |  |  |  |  |  |  |
Series A Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding |  |  |  |  | 30,227,056 | 0 |  |  | 0 |  |  | 30,227,056 |  | 30,227,056 | 30,227,056 |  |
Number of preferred shares converted to common shares |  |  |  |  | 30,227,056 |  |  |  |  |  |  |  |  |  |  |  |
Series B Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding |  |  |  |  | 23,288,783 |  |  |  |  |  |  |  |  |  |  |  |
Number of preferred shares converted to common shares |  |  |  |  | 23,288,783 |  |  |  |  |  |  |  |  |  |  |  |
Convertible Preferred Stock Series B-1 Upon Conversion [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares outstanding |  |  |  |  | 3,714,580 |  |  |  |  |  |  |  |  |  |  |  |
Number of preferred shares converted to common shares |  |  |  |  | 3,714,580 |  |  |  |  |  |  |  |  |  |  |  |
Convertible Preferred Stock Series B-2 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary Shares Outstanding |  |  |  |  | 3,301,849 |  |  |  |  |  |  |  |  |  |  |  |
Number of preferred shares converted to common shares |  |  |  |  | 3,571,427 |  |  |  |  |  |  |  |  |  |  |  |
Series C Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary Shares Outstanding |  |  |  |  | 31,046,360 |  |  |  |  |  |  |  |  |  |  |  |
Number of preferred shares converted to common shares |  |  |  |  | 34,420,469 |  |  |  |  |  |  |  |  |  |  |  |
Series C-1 Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary Shares Outstanding |  |  |  |  | 3,857,143 |  |  |  |  |  |  |  |  |  |  |  |
Number of preferred shares converted to common shares |  |  |  |  | 4,537,814 |  |  |  |  |  |  |  |  |  |  |  |
Director [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ordinary shares, shares authorized |  |  |  |  |  |  |  |  |  |  |  |  | 800,000,000 |  |  |  |
Ordinary shares, par value | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.0001 |  |  |  |
Common stock value authorized | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |  |  |
Board of Directors [Member] | American Depositary Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement Line Item [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of stock repurchase | $ |  |  |  |  |  |  |  |  |  |  | $ 20,000,000 |  |  |  |  |  |
Prepaid Expensestock repurchase program |  |  |  |  |  |  |  |  |  | ¥ 34,051 | $ 5,000,000 |  |  |  |  |  |
shares were repurchased |  |  |  |  |  | 0 |  |  | 0 |  |  |  |  |  |  |  |

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