Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Long-term debt
Total debt	$ 789.2	$ 800.4
Less current maturities	2.9	2.9
Total long-term debt	786.3	797.5
VALHI, INC. | Contran Credit Facility
Long-term debt
Total debt	313.0	314.3
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due September 15, 2025 | Kronos International, Inc
Long-term debt
Total debt	443.2	452.4
Tremont | Promissory Note
Long-term debt
Total debt	8.7	9.4
BMI | Bank loan | Western Alliance Bank
Long-term debt
Total debt	18.0	18.0
LandWell | Unsecured Debt
Long-term debt
Total debt	2.1	2.1
Other Subsidiary | Other
Long-term debt
Total debt	4.2	4.2
Subsidiary
Long-term debt
Total debt	$ 476.2	$ 486.1