v3.10.0.1
Summary of significant accounting policies - Foreign currency translation (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Foreign Currency Translation    
Cumulative foreign currency translation adjustments, net of tax in accumulated other comprehensive income $ (1,223) $ (898)
Income tax effect related to foreign currency translation adjustments $ 0 $ 0