Shareholders’ equity (deficit) - Share-based compensation - Non-vested share options (Details) - $ / shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Number of options
Non-vested at beginning of period	1,706,303	451,113
Forfeited/expired		(12,198)
Vested, outstanding	(336,405)	(217,018)
Non-vested share options at end of period	1,728,015	1,192,122
Weighted average fair value
Non-vested at beginning of period	$ 1.3458	$ 1.0266
Forfeited/expired		1.0639
Vested, outstanding	1.2104	1.0851
Non-vested at end of period	$ 3.5297	$ 1.1011
2011 Plan
Number of options
Granted	116,739	970,225
Weighted average fair value
Granted	$ 6.6491	$ 1.1343
2019 Plan
Number of options
Granted	241,378
Weighted average fair value
Granted	$ 14.2264