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Long-Term Debt - Valhi Contran Credit Facility - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jan. 26, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total long-term debt	$ 1,061.7		$ 1,041.5
Snake River
Debt Instrument [Line Items]
Total long-term debt	250.0
Contran Credit Facility \| Waste Management
Debt Instrument [Line Items]
Noncash borrowings	$ 36.3	$ 36.3
VALHI, INC. \| Contran Credit Facility
Debt Instrument [Line Items]
Debt instrument, Interest rate at period end	6.00%
Debt instrument, average interest rate during period	5.62%
Amount available for borrowing	$ 39.4
WCS \| Contran Credit Facility \| Contran \| Amounts Acquired in Business Divestiture
Debt Instrument [Line Items]
Acquired trade receivable	$ 36.3	$ 36.3