Shareholders’ equity (deficit) - Additional paid-in capital (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Additional paid-in capital
Balance at the beginning of period	$ 83,548	$ 25,985
Share-based compensation expense	1,191	633
Exercise of stock options	44	461
Balance at the end of period	114,917	83,548
Additional paid-in capital
Additional paid-in capital
Balance at the beginning of period	2,655	2,372
Share-based compensation expense	1,191	633
Exercise of stock options	(41)	(350)
Balance at the end of period	$ 3,805	$ 2,655