Share-based compensation - Summary of Status of Company's Stock Option Plan (Details) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Shares
Outstanding at beginning of period	7,042,377	4,415,397	4,415,397
-Cancelled			(527,820)
-Exercised			(10,000)
-Granted	0	258,500	3,164,800
Outstanding at end of period	7,042,377		7,042,377
Weighted Average Exercise Price
Outstanding at beginning of period	$ 1.01	$ 1.20	$ 1.20
-Cancelled			1.23
-Exercised			0.89
-Granted			0.79
Outstanding at end of period	$ 1.01		$ 1.01