Net loss per share - Basic and diluted net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (66,819)	$ (51,010)	$ (30,608)
Denominator:
Weighted average ordinary shares outstanding, basic	25,061,734	19,145,938	11,045,370
Weighted average ordinary shares outstanding, diluted	25,061,734	19,145,938	11,045,370
Net loss per share, basic	$ (2.67)	$ (2.66)	$ (2.77)
Net loss per share, diluted	$ (2.67)	$ (2.66)	$ (2.77)