Significant agreements - Deferred revenue (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Deferred revenue
Contract assets	$ 0	$ 0
Deferred revenue	61,873,000	71,340,000	$ 35,156,000
Ionis
Deferred revenue
Deferred revenue	21,489,000	34,115,000	3,000,000
Ionis | Deferred revenue material rights option
Deferred revenue
Deferred revenue	3,400,000
Genentech
Deferred revenue
Deferred revenue	39,308,000	34,436,000	27,579,000
Genentech | Deferred revenue material rights option
Deferred revenue
Deferred revenue	27,300,000
AstraZeneca
Deferred revenue
Deferred revenue	1,076,000	$ 2,361,000	$ 3,756,000
AstraZeneca | Target 4 and Target 5 Material Rights
Deferred revenue
Deferred revenue	$ 1,100,000