Net loss per share - Securities excluded from the diluted per share calculation (Details) - shares	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Antidilutive securities
Antidilutive securities (in shares)	4,950,608	3,726,338
Warrants to subscribe for convertible preferred shares (as adjusted to reflect the impact of the share capital reorganization and issuance of bonus shares
Antidilutive securities
Antidilutive securities (in shares)	50,000	71,450
Remaining warrants exercisable	71,450
Options to purchase ordinary shares
Antidilutive securities
Antidilutive securities (in shares)	4,950,608	3,654,888

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=6371337&loc=d3e3550-109257

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