Long-term debt - Components of Long-Term Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Long-term debt
Revolving credit facility	$ 43.2	$ 10.0
Total debt	557.2	507.4
Less current maturities	81.2	78.3
Total long-term debt	476.0	429.1
Subordinated, Unsecured Term Loan from Contran
Long-term debt
Subordinated debt	53.7	53.7
Kronos International, Inc | 9.50% Senior Secured Notes due 2029
Long-term debt
Kronos International, Inc.	379.1	365.4
Kronos International, Inc | 3.75% Senior Secured Notes due 2025
Long-term debt
Kronos International, Inc.	$ 81.2	$ 78.3