Significant agreements - Dementia Discovery Fund Agreement (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Dec. 31, 2020	May 31, 2019	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Significant agreements.
Potential milestone payments			$ 500		$ 500
Collaboration revenues			1,785	$ 1,571	3,593	$ 2,700
Deferred revenue	$ 35,156		34,074		34,074		$ 5,657
Dementia Discovery Fund
Significant agreements.
Upfront cash payment		$ 1,100
Potential milestone payments		$ 700
Threshold period for exercising option to establish a jointly-owned new company		90 days
Option to purchase ownership of new entity		34.00%
Threshold period of notice required for termination of agreement		60 days
Transaction price		$ 1,100
Collaboration revenues			154	$ 56	237	$ 112
Deferred revenue	821		$ 595		$ 595
Dementia Discovery Fund | NewCo
Significant agreements.
Option to purchase ownership of new entity		66.00%
Threshold period in which Newco shall have the right to initiate a new research program		2 years
Dementia Discovery Fund | NewCo | Maximum
Significant agreements.
Total voting rights related to ownership interests		50.00%
Specific scientific criteria milestone | Dementia Discovery Fund
Significant agreements.
Milestone payment received	$ 500