Summary of significant accounting policies - Foreign currency translation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Foreign currency translation
Cumulative foreign currency translation adjustments, net of tax in accumulated other comprehensive income	$ (1,295)	$ (898)
Income tax effect related to foreign currency translation adjustments	$ 0	$ 0

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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