Net loss per share - Calculation of 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 attributable to common stockholders	$ (80,026)	$ (77,620)	$ (69,703)
Denominator:
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic (in shares)	54,972,827	33,384,438	27,096,379
Weighted-average shares used in computing net loss per share attributable to common stockholders, diluted (in shares)	54,972,827	33,384,438	27,096,379
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (1.46)	$ (2.33)	$ (2.57)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (1.46)	$ (2.33)	$ (2.57)