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v3.21.1

Short-Term Investments (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract] |
Short Term Investments |
|  | December 31 |
|  | 2019 |  |  | 2020 |
|  | US$ |  |  | US$ |
Trading securities |  |  | 2,010 |  |  |  | — |

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