Related party transactions (Schedule of Related Parties Balances) (Details) - USD ($)		Mar. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Amounts due to a related party	[1]	$ 18,995,751	$ 18,365,738
Mr. Jie Han [Member]
Related Party Transaction [Line Items]
Amounts due to a related party	[1]	10,098,760	9,907,915
Mr. Jie Han's wife [Member]
Related Party Transaction [Line Items]
Amounts due to a related party	[1]	3,232,606	3,180,965
Mr. Jie Han's son [Member]
Related Party Transaction [Line Items]
Amounts due to a related party	[1]	742,556	728,523
Senior Managements [Member]
Related Party Transaction [Line Items]
Amounts due to a related party	[2]	$ 4,921,829	$ 4,548,335

[1] During the year ended December 31, 2018, the Company received RMB68.0 million (equivalent to US$10.1 million) from Mr. Jie Han, the Chairman of the Company, RMB21.8 million (equivalent to US$3.2 million) from Ms. Limei Sun, the wife of Mr. Jie Han, RMB5.0 million (equivalent to US$0.7 million) from Mr. Tiexin Han, the son of Mr. Jie Han.

[2] In August 2018, the Company received RMB10.0 million (equivalent to US$1.5 million) each from three senior management employees (Messers Junjie Ma, Yuchong Jia, Guangjun Jiao) of Sichuan Xinda as interest-free advances to Sichuan Xinda. During the year ended December 31, 2018, the Company also received RMB1.2 million (equivalent to US$0.2 million) from a senior management employee (Mr. Rujun Dai) of HLJ Xinda Group as interest-free advances to HLJ Xinda Group. During the three-month period ended March 31, 2019, the Company received another RMB1.9 million (equivalent to US$0.3 million) from Mr. Rujun Dai.