Income taxes - Reconciliation of federal tax rate to the effective rate (Details)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income taxes
U.S. statutory federal rate	21.00%	21.00%	21.00%
State taxes, net of federal effect	0.72%	2.88%	8.88%
Foreign rate differential	11.45%	5.71%	25.57%
Research and development tax credit			(1.92%)
Permanent items	0.46%	(0.32%)	(0.70%)
Change in valuation allowance		(0.08%)	2.38%
Total U.S. statutory federal tax rate to the effective rate	10.73%	17.77%	4.07%