Related party transactions (Narrative) (Details)		Mar. 31, 2019 USD ($)	Mar. 31, 2019 CNY (¥)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 CNY (¥)	Aug. 31, 2018 USD ($)	Aug. 31, 2018 CNY (¥)
Receivable, Related Parties	[1]	$ 7,425,559		$ 7,285,231
Sichuan Xinda [Member]
Receivable, Related Parties						$ 1,500,000
Sichuan Xinda [Member] | China, Yuan Renminbi [Member]
Receivable, Related Parties | ¥							¥ 10,000,000
Mr. Jie Han [Member]
Receivable, Related Parties				10,100,000
Mr. Jie Han [Member] | China, Yuan Renminbi [Member]
Receivable, Related Parties | ¥					¥ 68,000,000
Mr. Limei Sun [Member]
Receivable, Related Parties				3,200,000
Mr. Limei Sun [Member] | China, Yuan Renminbi [Member]
Receivable, Related Parties | ¥					21,800,000
Mr. Tiexin Han [Member]
Receivable, Related Parties				700,000
Mr. Tiexin Han [Member] | China, Yuan Renminbi [Member]
Receivable, Related Parties | ¥					5,000,000
Senior Management [Member]
Receivable, Related Parties		$ 300,000		$ 200,000
Senior Management [Member] | China, Yuan Renminbi [Member]
Receivable, Related Parties | ¥			¥ 1,900,000		¥ 1,200,000

[1] On December 18, 2018, HLJ Xinda Group entered into an agreement with Mr. Xiaohui Gao, General Manager of Heilongjiang Xinda Enterprise Group Shanghai New Materials Sales Company Limited ("Shanghai Sales"), to transfer the wholly owned equity from HLJ Xinda Group to Mr. Gao for a total consideration of RMB50.0 million (equivalent to US$7.4 million). Pursuant to the contract, the Company completed the legal transfer on December 19, 2018 and the full consideration of $7.4 million was received on April 11, 2019.