Shareholders’ equity (deficit) - Share-based compensation - Non-vested share options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of options
Non-vested at beginning of period	1,706,303
Exercised	(33,162)
Non-vested share options at end of period	1,371,275	1,706,303
Weighted average fair value
Non-vested at beginning of period	$ 1.346	$ 1.027
Exercised	1.3260	1.2870
Non-vested at end of period	$ 3.889	$ 1.346
2011 Plan
Number of options
Non-vested at beginning of period	1,706,303	451,113
Forfeited/expired	(14,099)	(12,198)
Granted	116,742	1,695,258
Exercised	(33,162)	(356,797)
Vested, outstanding	(656,646)	(427,870)
Non-vested share options at end of period	1,152,300	1,706,303
Weighted average fair value
Forfeited/expired	$ 1.906	$ 1.064
Granted	6.6490	1.4630
Vested, outstanding	1.333	$ 1.479
Non-vested at end of period	$ 1.884
2019 Plan
Number of options
Forfeited/expired	(66,998)
Granted	287,138
Vested, outstanding	(1,165)
Non-vested share options at end of period	218,975
Weighted average fair value
Forfeited/expired	$ 12.221
Granted	13.9120
Vested, outstanding	12.160
Non-vested at end of period	$ 14.439