Segment information (Details 2) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 64,923,960	$ 51,699,930	$ 114,707,413	$ 93,566,778
China Mainland [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	32,880,005	32,086,138	61,185,768	54,247,730
Asia, others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	25,183,900	12,092,612	40,938,296	25,788,170
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	4,849,360	3,612,677	9,387,263	8,465,407
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	1,998,243	3,604,935	3,163,074	4,663,067
Others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 12,452	$ 303,568	$ 33,012	$ 402,404