Significant agreements - Collaboration revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Significant agreements
Collaboration revenues	$ 1,522	$ 1,661	$ 7,906	$ 4,469
AstraZeneca
Significant agreements
Collaboration revenues	362	391	787	691
Sanofi
Significant agreements
Collaboration revenues	57	1,093	6,016	2,219
Oxurion
Significant agreements
Collaboration revenues	0	177	0	1,559
Dementia Discovery Fund
Significant agreements
Collaboration revenues	103	0	103	0
Material transfer agreement
Significant agreements
Collaboration revenues	$ 1,000	$ 0	$ 1,000	$ 0