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Income taxes (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2017
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2019
Income Tax Disclosure [Line Items]        
Federal corporate tax rate     35.00%  
Income tax benefit resulting from re-measurement of deferred taxes $ (251)      
Forecast [Member]        
Income Tax Disclosure [Line Items]        
Federal corporate tax rate   21.00%   21.00%