Prepaid expenses and other current assets (Narrative) (Details)		1 Months Ended
		Mar. 31, 2019 USD ($)	Mar. 31, 2019 CNY (¥)	Apr. 11, 2019 USD ($)	Mar. 31, 2019 CNY (¥)	Dec. 31, 2018 USD ($)
Receivable, Related Parties	[1]	$ 7,425,559				$ 7,285,231
Consideration for sales of Shanghai Sales [Member]
Receivable, Related Parties		7,400,000
Consideration for sales of Shanghai Sales [Member] | Subsequent Event [Member]
Receivable, Related Parties				$ 7,400,000
Consideration for sales of Shanghai Sales [Member] | China, Yuan Renminbi [Member]
Receivable, Related Parties | ¥					¥ 50,000,000
Shanghai Sales [Member]
Prepaid		16,100,000
Amount paid by Shanghai Sales to HLJJXinda		$ 16,100,000
Shanghai Sales [Member] | China, Yuan Renminbi [Member]
Prepaid | ¥			¥ 108,300,000
Amount paid by Shanghai Sales to HLJJXinda | ¥			¥ 108,300,000

[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.