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Long-Term Debt - Kronos Term Loan - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 6 Months Ended 8 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2017
Jun. 30, 2017
Sep. 13, 2017
Sep. 30, 2017
Debt Instrument [Line Items]          
Loss on prepayment of debt   $ 7.1     $ 7.1
Kronos Worldwide, Inc. | Notes Payable, Other Payables | 2014 Term Loan          
Debt Instrument [Line Items]          
Quarterly principal payment     $ 1.8    
Debt instrument, voluntary repayment period         2017-09
Repayments of debt $ 338.6        
Loss on prepayment of debt   7.1      
Termination of interest rate swap contract   3.3      
Write-off of unamortized debt issuance costs   2.7      
Write-off of unamortized original issue discount   $ 0.7      
Debt instrument, average interest rate during period       4.10%