Quarterly report pursuant to Section 13 or 15(d)

Inventories (Details)

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Inventories (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Inventories          
Finished goods $ 7,173,516   $ 7,173,516   $ 5,489,360
Work in process 381,840   381,840   470,187
Raw materials 2,126,763   2,126,763   1,356,395
Inventories 9,682,119   9,682,119   $ 7,315,942
Inventory write-downs $ 326,000 $ 370,000 $ 582,034 $ 680,851