Significant agreements - Summary of Contract Assets and Liabilities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Contract liabilities:
Beginning Balance	$ 35,156,000	$ 5,657,000
Additions	49,056,000	35,085,000
Deductions	(11,697,000)	(8,028,000)	$ (10,413,000)
Impact of Exchange Rates	(1,175,000)	2,442,000
Ending Balance	71,340,000	35,156,000	5,657,000
Contract assets
Contract assets	0	0
Ionis
Contract liabilities:
Beginning Balance	3,000,000
Additions	36,002,000
Deductions	(4,242,000)
Impact of Exchange Rates	(645,000)
Ending Balance	34,115,000	3,000,000
Genentech
Contract liabilities:
Beginning Balance	27,579,000
Additions	13,000,000	31,000,000
Deductions	(5,660,000)	(4,896,000)
Impact of Exchange Rates	(483,000)	1,475,000
Ending Balance	34,436,000	27,579,000
Dementia Discovery Fund
Contract liabilities:
Beginning Balance	821,000	744,000
Additions		500,000
Deductions	(391,000)	(436,000)
Impact of Exchange Rates	(2,000)	13,000
Ending Balance	428,000	821,000	744,000
AstraZeneca
Contract liabilities:
Beginning Balance	3,756,000	4,913,000
Additions	54,000	585,000
Deductions	(1,404,000)	(2,696,000)
Impact of Exchange Rates	(45,000)	954,000
Ending Balance	2,361,000	3,756,000	$ 4,913,000
Ionis Evaluation and Option Agreement
Contract liabilities:
Beginning Balance	$ 3,000,000
Additions		3,000,000
Ending Balance		$ 3,000,000