Net loss per share - Securities excluded from the diluted per share calculation (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Antidilutive securities
Antidilutive securities (in shares)	4,603,486	3,736,663	2,727,231
Remaining warrants exercisable				80,000
Warrants to subscribe for ordinary shares
Antidilutive securities
Antidilutive securities (in shares)			92,885
Remaining warrants exercisable			65,000
Options to purchase ordinary shares
Antidilutive securities
Antidilutive securities (in shares)	4,603,486	3,736,663	2,634,346
Number of ordinary shares for warrants exercise			92,885