Fair value of financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash equivalents	$ 91,916	$ 109,155
Note receivable	150	150
Total	92,066	109,305
Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash equivalents	91,916	109,155
Total	91,916	109,155
Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Note receivable	150	150
Total	$ 150	$ 150