Segment reporting (Details) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2025 USD ($)	Jun. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2025 USD ($) segment	Sep. 30, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment							1
Revenue from collaboration agreements	$ 11,230			$ 15,362			$ 24,931	$ 30,407
General and administrative	8,920			11,768			27,017	31,751
Total operating expenses	45,642			43,606			117,008	112,312
Non-operating income	(2,246)			(3,578)			(7,569)	(11,162)
Net loss	(32,166)	$ (26,020)	$ (26,322)	(24,666)	$ (17,716)	$ (28,361)	(84,508)	(70,743)
Reportable Segment
Segment Reporting Information [Line Items]
Revenue from collaboration agreements	0			0			0	0
Reportable Segment | Operating Segments
Segment Reporting Information [Line Items]
Development expenses	12,885			18,407			40,040	41,053
Research expenses	8,253			8,048			24,823	22,855
General and administrative	9,178			8,320			26,320	24,540
Total operating expenses	30,316			34,775			91,183	88,448
Non-operating income	(2,246)			(3,578)			(7,569)	(11,162)
Adjustments or reconciling items	4,096			(6,531)			894	(6,543)
Net loss	$ (32,166)			$ (24,666)			$ (84,508)	$ (70,743)