Income taxes - Reconciliation of Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax credit at the federal and state statutory rate	$ (2,219,152)	$ (1,288,471)
Foreign taxation	121,579	(1,325,577)
Permanent differences	1,280,902	1,606,144
Foreign net operating losses utilized	(19,347)
Foreign tax differential		(203,943)
Valuation allowance	938,250	1,211,846
Net future tax asset	$ 102,232	$ 0