Net loss per share - Basic and diluted net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net loss attributable to ordinary shareholders	$ (16,191)	$ (11,324)
Denominator:
Weighted average ordinary shares outstanding, basic and diluted	22,100,840	17,997,929
Net loss per share attributable to ordinary shareholders, basic and diluted	$ (0.73)	$ (0.63)