Significant agreements - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Contract assets
Beginning Balance			$ 0	$ 0	$ 0
Additions					0
Deductions					0
Impact of Exchange Rates					0
Ending Balance					0
Contract liabilities:
Beginning Balance			35,156	5,657	5,657
Additions			2,054		35,085
Deductions	$ (1,785)	$ (1,251)	(3,593)	(2,002)
Impact of Exchange Rates			457		2,442
Ending Balance	34,074		34,074		35,156
Deductions			(3,593)		(8,028)
AstraZeneca
Contract liabilities:
Beginning Balance			3,756	4,913	4,913
Additions			54		585
Impact of Exchange Rates			40		954
Ending Balance	3,573		3,573		3,756
Deductions			(277)		(2,696)
Dementia Discovery Fund
Contract assets
Beginning Balance			821	744	744
Additions					500
Deductions					(436)
Impact of Exchange Rates					13
Ending Balance					821
Contract liabilities:
Beginning Balance			821
Impact of Exchange Rates			11
Ending Balance	595		595		821
Deductions			(237)
Genentech
Contract assets
Beginning Balance			27,579	0	0
Additions					31,000
Deductions					(4,896)
Impact of Exchange Rates					1,475
Ending Balance					27,579
Contract liabilities:
Beginning Balance			27,579
Additions			2,000
Impact of Exchange Rates			367
Ending Balance	26,867		26,867		27,579
Deductions			(3,079)
Ionis Evaluation and Option Agreement
Contract assets
Beginning Balance			3,000	$ 0	0
Additions					3,000
Deductions					0
Impact of Exchange Rates					0
Ending Balance					3,000
Contract liabilities:
Beginning Balance			3,000
Impact of Exchange Rates			39
Ending Balance	$ 3,039		$ 3,039		$ 3,000