Long-Term Debt - Valhi Contran Credit Facility - Additional Information (Detail) - Contran Credit Facility - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Jan. 26, 2018
Waste Management
Debt Instrument [Line Items]
Noncash borrowings	$ 36.3	$ 36.3
VALHI, INC.
Debt Instrument [Line Items]
Debt instrument, Interest rate at period end	5.75%
Debt instrument, average interest rate during period	5.53%
Amount available for borrowing	$ 39.4
WCS \| Contran \| Amounts Acquired in Business Divestiture
Debt Instrument [Line Items]
Acquired trade receivable	$ 36.3	$ 36.3

The average effective interest rate during the reporting period.

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