Ordinary shares - Share Purchase Agreement (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Oct. 15, 2021	Jul. 09, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Net proceeds			$ 7,558
Offering expenses			16,100	$ 1,900	$ 8,500
Aggregate purchase price			290,984	$ 48,144	$ 56,381
American Depositary Shares
Class of Stock [Line Items]
Gross proceeds before discounts and commissions	$ 201,300
Net proceeds	$ 188,400
Ionis Share Purchase Agreement
Class of Stock [Line Items]
Aggregate purchase price			$ 7,558
At the market offering
Class of Stock [Line Items]
Shares issued (in shares)			3,771,684	2,928,813
Gross proceeds before discounts and commissions			$ 105,800	$ 50,000
Net proceeds			102,600	48,100
Offering expenses			$ 3,200	$ 1,900
Underwritten Public Offering | American Depositary Shares
Class of Stock [Line Items]
Shares issued (in shares)	3,726,852
Price per share	$ 54.00
Ionis | Ionis Share Purchase Agreement
Class of Stock [Line Items]
Shares issued (in shares)		282,485
Price per share		$ 38.94
Aggregate purchase price		$ 11,000
Fair value of shares held		$ 7,600
Ionis | Ionis Share Purchase Agreement | American Depositary Shares
Class of Stock [Line Items]
Price per share		$ 31.11