Fair value of financial instruments - Hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Hierarchy for financial instruments measured at fair value on a recurring basis
Short-term investments	$ 3,992	$ 8,064
Derivative liability (see Note 11)	1,231	1,135
Recurring basis | Fair Value
Hierarchy for financial instruments measured at fair value on a recurring basis
Cash and cash equivalents	27,858	16,830
Short-term investments	3,992	8,064
Total financial assets	31,850	24,894
Earnout liability	30	30
Derivative liability (see Note 11)	1,231	1,135
Total financial liabilities	1,261	1,165
Recurring basis | Fair Value | Level 1
Hierarchy for financial instruments measured at fair value on a recurring basis
Cash and cash equivalents	25,357	12,338
Short-term investments		1,261
Total financial assets	25,357	13,599
Recurring basis | Fair Value | Level 2
Hierarchy for financial instruments measured at fair value on a recurring basis
Cash and cash equivalents	2,501	4,492
Short-term investments	3,992	6,803
Total financial assets	6,493	11,295
Recurring basis | Fair Value | Level 3
Hierarchy for financial instruments measured at fair value on a recurring basis
Earnout liability	30	30
Derivative liability (see Note 11)	1,231	1,135
Total financial liabilities	$ 1,261	$ 1,165