Commitments and contingencies - Components of operating lease expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Operating lease expense:
Total operating lease expense	$ 94
Other information:
Cash paid for amounts included in the measurment of operating lease liability	$ 59
Weighted average remaining lease term	1 year
Weighted average discount rate	8.00%
General and administrative expense
Operating lease expense:
Fixed operating lease expense	$ 59
Variable operating lease expense	27
Research and development expense
Operating lease expense:
Short-term lease expense	$ 8