Income taxes - Reconciliation of federal tax rate to the effective rate (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income taxes
U.S. statutory federal rate	21.00%	21.00%
State taxes, net of federal effect	8.88%	2.72%
Nontaxable foreign income	(25.57%)	(43.36%)
Research & Development Tax Credit	(1.92%)	(7.39%)
Permanent items	(0.70%)	(6.26%)
Goodwill impairment		20.31%
Valuation allowance for deferred tax assets	2.38%	0.65%
Total U.S. statutory federal tax rate to the effective rate	4.07%	(12.33%)