Income taxes - Federal income tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Income taxes
Federal tax benefit at statutory rate	$ (44,603)
Change in valuation allowance	46,139
Share-based compensation	3,402
Other nondeductible items	379
Research and development credits	(5,345)
Other	28
Total	$ 0	$ 0
Federal tax benefit at statutory rate, percent	21.00%	21.00%
State tax, net of federal benefit, percent		0.50%
Change in valuation allowance, percent	(21.70%)	(22.80%)
Share-based compensation, percent	(1.60%)
Share-based compensation, percent		(0.70%)
Other nondeductible items, percent	(0.20%)
Research and development credits, percent	2.50%	2.10%
Other, percent	0.00%	(0.10%)