Stock based compensation - Schedule of share based expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based expenses	$ 361	$ 244	$ 1,188	$ 848
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based expenses	275	135	638	561
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based expenses	$ 86	$ 109	$ 550	$ 287