Income taxes - Reconciliation of benefit for income taxes (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income taxes
Benefit for income taxes at statutory rate	19.00%	19.00%	19.00%
(Decreases) increases resulting from:
Federal tax credits	0.30%	0.60%	0.90%
Change in valuation allowance	(16.80%)	(27.00%)	(15.40%)
Net losses surrendered for research credit	6.50%	5.90%	6.20%
Impact of statutory rate change	11.30%	12.10%	1.80%
Impact of foreign exchange rates	(9.90%)		1.30%
Other	3.90%	3.60%
Effective income tax rate	1.30%	2.40%	1.40%