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Inventories (Tables)
9 Months Ended
Sep. 30, 2019
Inventories [Abstract]  
Schedule of inventories
   December 31,   September 30, 
   2018   2019 
Raw materials  $1,675,383   $1,422,821 
Work in progress   2,737,415    1,089,938 
Finished goods   5,209,563    8,366,042 
   $9,622,361   $10,878,801