Commitments and contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Commitments and contingencies
Security deposit	$ 20	$ 20
Initial lease term under the agreement	6 months
Extension lease term under the agreement	6 months
Rent expense	$ 305
Rent expense		$ 12
Total future minimum commitments	401
2020	321
2021	80
Non-cancelable purchase commitments with contract research organizations and contract manufacturing organizations	$ 4,358