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Short-Term Investments
12 Months Ended
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.