Subsequent events (Details) $ / shares in Units, $ in Thousands, £ in Millions				1 Months Ended	3 Months Ended				9 Months Ended
	Nov. 01, 2021 GBP (£)	Oct. 15, 2021 USD ($) $ / shares shares	Feb. 21, 2020 USD ($)	Oct. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 shares
Subsequent events
Issuance of ADSs gross proceeds					$ 29,843	$ 13,977	$ 58,775	$ 46,323
Genentech
Subsequent events
Expansion Fee			$ 10,000
At the market offering
Subsequent events
Shares issued (in shares) | shares									6,700,497
Subsequent events | Office and laboratory space in U.K.
Subsequent events
Leases, term of contract	10 years
Option to renew	true
Renewal term	10 years
Subsequent events | Office and laboratory space in U.K. | Maximum
Subsequent events
Annual rent | £	£ 2.2
Subsequent events | Genentech
Subsequent events
Expansion Fee				$ 10,000
Subsequent events | American Depositary Shares
Subsequent events
Issuance of ADSs gross proceeds		$ 201,300
Subsequent events | Underwritten Public Offering | American Depositary Shares
Subsequent events
Shares issued (in shares) | shares		3,726,852
Price per share | $ / shares		$ 54.00