Net loss per share - Securities excluded from the diluted per share calculation (Details) - shares	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Antidilutive securities
Antidilutive securities (in shares)	5,567,066	4,950,608
Restricted ordinary shares
Antidilutive securities
Antidilutive securities (in shares)	187,725
Options to purchase ordinary shares
Antidilutive securities
Antidilutive securities (in shares)	5,379,341	4,950,608

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration