v3.20.4
Summary of significant accounting policies - Foreign currency translation (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Foreign currency translation      
Cumulative foreign currency translation adjustments, net of tax in accumulated other comprehensive loss $ (2,280) $ (1,447)  
Income tax effect related to foreign currency translation adjustments 0 0  
Foreign currency translation gain (loss) $ 0 $ 0 $ 0