Fair Value Measurements and Financial Instruments - Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Kronos Worldwide, Inc. | Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	$ 343.5	$ 345.9
Long term debt, fair value	344.3	341.5
VALHI, INC. | Notes Payable, Other Payables | Snake River
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	250.0	250.0
Long term debt, fair value	250.0	250.0
VALHI, INC. | Contran Credit Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	248.6	223.7
Long term debt, fair value	248.6	223.7
WCS | Fixed Rate Loans
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	66.0	67.1
Long term debt, fair value	66.0	67.1
Tremont | Promissory Note
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	17.3	17.4
Long term debt, fair value	17.3	17.4
BMI | Bank note payable
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	9.6	10.3
Long term debt, fair value	9.6	10.3
LandWell | Unsecured Debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	3.1	3.1
Long term debt, fair value	3.1	3.1
Reported Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	257.7	280.3
Deferred payment obligation	8.7	8.5
Portion at Fair Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	257.7	280.3
Deferred payment obligation	$ 8.7	$ 8.5