Gains on disposal of a subsidiary (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains on disposal of subsidiary	$ 518,491
Consideration for sales of Shanghai New Materials [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains on disposal of subsidiary	$ 500,000