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Short-Term Investments | 12 Months Ended
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Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract] |
Short-Term Investments | 4. SHORT-TERM INVESTMENTS
|  | December 31 |
|  | 2019 |  |  | 2020 |
|  | US$ |  |  | US$ |
Trading securities |  |  | 2,010 |  |  |  | — |
The Company classified certain short-term investments as trading securities. Realized gains on sales of these trading securities were US$134 thousand, US$48 thousand and US$169 thousand for the years ended December 31, 2018, 2019 and 2020, respectively . The amount of unrealized losses related to trading securities at year end was nil for the years ended December 31, 2018, 2019 and 2020, respectively.

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