Shareholders’ equity - Stock-based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average exercise price (in USD per share)	$ 4.39	$ 3.31
Restricted stock units granted during period (in shares)	371,500	901,900
Grant date fair value (in USD per share)	$ 4.39	$ 3.29
Allocated share-based compensation expense	$ 1,322	$ 1,293
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	416	555
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 906	$ 738
Arbutus Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted during period (in shares)	952,400	3,943,722