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Notes and Accounts Receivable
12 Months Ended
Dec. 31, 2020
Receivables [Abstract]  
Notes and Accounts Receivable
5. NOTES AND ACCOUNTS RECEIVABLE
 
    
December 31
 
    
2019
    
2020
 
    
US$
    
US$
 
Trade accounts receivable
     110,351        117,387  
Allowance for doubtful accounts
     (1,617      (1,561
    
 
 
    
 
 
 
       108,734        115,826  
    
 
 
    
 
 
 
The changes in allowance are summarized as follows:
 
    
Year Ended December 31
 
    
2018
    
2019
   
2020
 
    
US$
    
US$
   
US$
 
Allowance for doubtful accounts
                         
Balance, beginning of year
     598        645       1,617  
Additions (reversals) charged to expense, net
     47        1,164       15  
Write-offs
     —          (192     (71
    
 
 
    
 
 
   
 
 
 
Balance, end of year
     645        1,617       1,561