Income taxes - Components of income before income taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income taxes
Foreign (not subject to income taxes)	$ 5,780,692	$ 6,475,693
Mexico	(1,767,915)	(4,903,988)
United States	(2,952,265)	2,956,552
Income before income taxes	1,060,512	4,528,257
Less discontinued operations		4,902,243
Income before income taxes	$ 3,634,591	$ 9,430,500