Net loss per share attributable to common stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net loss per share attributable to common stockholders
Net loss	$ (8,082)	$ (2,143)
Dividends accrued on redeemable convertible preferred stock	(1,190)	(1,190)
Accretion of redeemable convertible preferred stock	(296)	(296)
Adjusted net loss attributable to common stockholders	$ (9,568)	$ (3,629)
Weighted average common shares used in net loss per share attributable to common stockholders, basic and diluted	2,706,133	2,288,875
Basic and diluted net loss per common share outstanding	$ (3.54)	$ (1.59)