Shareholders’ equity (deficit) - Share-based compensation - Outstanding and exercisable options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Outstanding and exercisable options, number of shares
Outstanding at beginning of period	2,295,045
Exercised	(33,162)
Outstanding at end of period	2,584,666	2,295,045
Exercisable at end of period	1,213,391
Outstanding and exercisable options, weighted average exercise price
Outstanding at beginning of period	$ 1.771	$ 1.133
Exercised	1.3260	1.2870
Outstanding at end of period	3.755	1.771
Exercisable at end of period	$ 1.652	$ 1.314
Weighted average remaining contractual life (in years)	7 years 9 months 18 days	8 years 7 months 6 days
Weighted average remaining contractual life for vested options (in years)	7 years	6 years 7 months 6 days
Options forfeited	81,097
Share-based compensation expense	$ 1,191	$ 633
Unrecognized compensation cost	$ 6,464	$ 2,402
Expected period for recognition	2 years 7 months 6 days	3 years 1 month 6 days
2011 Plan
Outstanding and exercisable options, number of shares
Outstanding at beginning of period	2,295,045	968,782
Forfeited/cancelled	(14,099)	(12,198)
Granted	116,742	1,695,258
Exercised	(33,162)	(356,797)
Outstanding at end of period	2,364,526	2,295,045
Exercisable at end of period	1,212,226	588,817
Outstanding and exercisable options, weighted average exercise price
Forfeited/expired	$ 2.660	$ 1.096
Granted	9.417	2.037
Outstanding at end of period	2.151
Exercisable at end of period	$ 1.637
Options forfeited	14,099
Weighted average fair values of options granted	$ 6.6490	$ 1.4630
2019 Plan
Outstanding and exercisable options, number of shares
Forfeited/cancelled	(66,998)
Granted	287,138
Outstanding at end of period	220,140
Exercisable at end of period	1,165
Outstanding and exercisable options, weighted average exercise price
Forfeited/expired	$ 17.224
Granted	19.948
Outstanding at end of period	20.777
Exercisable at end of period	$ 17.780
Options forfeited	66,998	12,198
Weighted average fair values of options granted	$ 13.9120