Net loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Numerator:
Net loss	$ (10,926)	$ (9,329)	$ (43,000)
Denominator:
Weighted-average common shares outstanding, basic and diluted	25,630,007	1,006,595
Net loss per share, basic and diluted	$ (0.43)	$ (9.27)