Fair value of financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash equivalents	$ 82,013	$ 102,749
Note receivable	150	150
Total	82,163	102,899
Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash equivalents	82,013	102,749
Total	82,013	102,749
Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Note receivable	150	150
Total	$ 150	$ 150