Income taxes - Components of Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income taxes
Net loss	$ (53,478,812)	$ (28,059,807)	$ (15,528,269)
Foreign
Income taxes
Net loss	(27,215,385)	(25,268,373)	(15,713,032)
Domestic
Income taxes
Net loss	$ (26,263,427)	$ (2,791,434)	$ 184,763