Significant agreements - Collaboration revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Significant agreements.
Collaboration revenues	$ 3,842	$ 614	$ 6,542	$ 8,520
AstraZeneca
Significant agreements.
Collaboration revenues	213	441	944	1,229
Sanofi
Significant agreements.
Collaboration revenues	0	0	0	6,016
Oxurion
Significant agreements.
Collaboration revenues	2,362	0	2,362	0
Dementia Discovery Fund
Significant agreements.
Collaboration revenues	58	173	170	275
Material transfer agreement
Significant agreements.
Collaboration revenues	0	0		$ 1,000
Genetech
Significant agreements.
Collaboration revenues	$ 1,209	$ 0	$ 3,066