Shareholders’ equity (deficit) - Share-based compensation - Outstanding and exercisable options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Outstanding and exercisable options, number of shares
Outstanding at beginning of period			2,295,045	968,782
Forfeited/cancelled				(12,198)
Exercised			(18,153)	(42,781)
Outstanding at end of period	2,635,009	1,884,028	2,635,009	1,884,028
Exercisable at end of period	906,994	691,983	906,994	691,983
Outstanding and exercisable options, weighted average exercise price
Outstanding at beginning of period			$ 1.7714	$ 1.1330
Forfeited/expired				1.0958
Granted			11.76	1.13
Exercised			1.3225	0.8298
Outstanding at end of period	$ 3.8141	$ 1.3671	3.8141	1.3671
Exercisable at end of period	$ 1.4851	$ 1.1064	$ 1.4851	$ 1.1064
Weighted average remaining contractual life (in years)			6 years 3 months	6 years 3 months
Weighted average remaining contractual life for vested options (in years)			6 years 8 months 12 days	7 years
Options forfeited			0	12,198
Share-based compensation expense	$ 350	$ 85	$ 837	$ 289
Unrecognized compensation cost	$ 6,193	$ 1,336	$ 6,193	$ 1,336
Expected period for recognition			2 years 9 months 18 days	3 years 1 month 6 days
2011 Plan
Outstanding and exercisable options, number of shares
Granted			116,739	970,225
Outstanding at end of period	2,393,631		2,393,631
Outstanding and exercisable options, weighted average exercise price
Granted			$ 9.4152	$ 1.5745
Weighted average fair values of options granted			$ 6.6491	$ 1.1343
2019 Plan
Outstanding and exercisable options, number of shares
Granted			241,378
Outstanding and exercisable options, weighted average exercise price
Granted			$ 20.3400
Weighted average fair values of options granted			$ 14.2264