Fair value of financial assets and liabilities - Financial assets and liabilities measured at fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value of financial assets and liabilities
Warrant liability		$ 4,804
Warrant liability
Fair value of financial assets and liabilities
Warrant liability	$ 0	4,804
Level 3
Fair value of financial assets and liabilities
Warrant liability		4,804
Level 3 | Warrant liability
Fair value of financial assets and liabilities
Warrant liability		$ 4,804