Subsequent events (Details Textual) - USD ($)		9 Months Ended
	Oct. 22, 2018	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Net proceeds from issuance of common stock		$ 597,743	$ 3,426,050
Subsequent Event [Member] | October 2018 Public Offering [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Stock issued during period, shares, new issues	2,220,000
Shares issued, price per share	$ 1.45
Gross proceeds from sale of common stock	$ 3,200,000
Net proceeds from issuance of common stock	$ 2,800,000
Subsequent Event [Member] | Underwriters Overallotments [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Period option granted to the underwriters to acquire an additional shares to cover overallotments	45 days
Additional share issued	330,751