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Trade Accounts and Bills Receivable, Net (Tables)
6 Months Ended
Jun. 30, 2019
Trade Accounts and Bills Receivable, net [Abstract]  
Schedule of trade accounts and bills receivable

   December 31,   June 30, 
   2018   2019 
Trade accounts receivable  $19,054,863   $19,102,558 
Less: Allowance for doubtful accounts   (3,657,173)   (3,984,050)
    15,397,690    15,118,508 
Bills receivable   6,353,342    2,188 
   $21,751,032   $15,120,696 

Schedule of analysis of the allowance for doubtful accounts
   December 31,   June 30, 
   2018   2019 
Balance at beginning of period  $3,700,922   $3,657,173 
Provision for the period   474,950    605,098 
Reversal - recoveries by cash   (312,462)   (281,160)
Charged to consolidated statements of operations and comprehensive (loss) income   162,488    323,938 
Foreign exchange adjustment   (206,237)   2,939 
Balance at end of period  $3,657,173   $3,984,050