Intangible assets amortization expenses (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Intangible assets amortization expenses        
Amortization expenses relating to intangible assets $ 65,643 $ 73,498 $ 199,609 $ 246,009