Commitments and contingencies (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 01, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2019
Commitments and contingencies
Monthly lease payments payable under the amended agreement	$ 19
Increase in rental expense (as a percentage)	3.00%
Security deposit		$ 20	$ 20	$ 20
Initial lease term under the agreement		6 months	6 months	6 months
Extension lease term under the agreement		6 months	6 months	6 months
Monthly lease payments under the agreement		$ 4
Rent expense			$ 87	$ 230
Non-cancelable purchase commitments with contract research organizations and contract manufacturing organizations		$ 6,158	$ 6,158	$ 6,158