Income taxes - Reconciliation of federal tax rate to the effective rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income taxes
U.S. statutory federal rate	21.00%	21.00%
State taxes, net of federal effect	2.72%	4.00%
Nontaxable foreign income	(43.36%)	(17.28%)
Research & Development Tax Credit	(7.39%)	(11.73%)
Permanent items	(6.26%)	(0.67%)
Goodwill impairment	20.31%
Valuation allowance for deferred tax assets	0.65%	5.60%
Effective Income Tax Rate Reconciliation, Percent	(12.33%)	0.92%