Segment information (Details 2) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 293,931,961	$ 244,166,312
China Mainland [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	142,429,214	139,096,630
Asia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	119,255,566	81,060,414
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	24,482,803	18,684,852
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	7,385,580	4,769,797
Others [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 378,798	$ 554,619