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Accounts receivable, net (Details 1) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Opening allowance for doubtful accounts $ 193,338 $ 193,338  
Provision for doubtful accounts 0 42,553 $ 0
Accounts written off during the year (34,436) (42,553)  
Ending allowance for doubtful accounts $ 158,902 $ 193,338 $ 193,338