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Income taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Parenthetical) (Detail) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Income Taxes [Line Items]      
Deferred tax assets   $ 14,653 $ 28,109
Litigation settlement expense $ 7,000    
Accrued Expenses and Other Current Liabilities [Member]      
Income Taxes [Line Items]      
Litigation settlement expense   4,000  
Accrued Expenses and Other Current Liabilities [Member] | TransUnion Risk and Alternative Data Solutions, Inc [Member]      
Income Taxes [Line Items]      
Deferred tax assets   $ 1,037