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Income taxes - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Income Taxes [Line Items]          
Statutory federal income tax rate 21.00% 34.00% 21.00% 34.00%  
Effective income tax rate, percentage 0.00% 0.00% 0.00% 0.00%  
Percentage of tax benefits likelihood of being realized upon settlement of tax authority     greater than 50%    
Unrecognized tax benefits $ 0   $ 0   $ 0
Interactive Data, LLC | State Tax Returns | Earliest Tax Year          
Income Taxes [Line Items]          
Open tax year for examination     2014