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Trade Accounts and Bills Receivable, Net (Tables)
3 Months Ended
Mar. 31, 2019
Trade Accounts and Bills Receivable, net [Abstract]  
Schedule of trade accounts and bills receivable
   December 31,   March 31, 
   2018   2019 
Trade accounts receivable  $19,054,863   $20,315,956 
Less: Allowance for doubtful accounts   (3,657,173)   (3,819,724)
    15,397,690    16,496,232 
Bills receivable   6,353,342    320,653 
   $21,751,032   $16,816,885 
Schedule of analysis of the allowance for doubtful accounts
   March 31,   March 31, 
   2018   2019 
Balance at beginning of period  $3,700,922   $3,657,173 
Provision for the period   11,199    241,549 
Reversal – recoveries by cash   (97,852)   (170,387)
Charged to consolidated statements of operations and comprehensive (loss) income   (86,653)   71,162 
Foreign exchange adjustment   134,903    91,389 
Balance at end of period  $3,749,172   $3,819,724