Long-term debt - Subordinated, Unsecured Term Loan from Contran (Details) € in Thousands, $ in Millions			1 Months Ended		12 Months Ended
	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Jul. 31, 2024	Feb. 29, 2024	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Sep. 15, 2025 EUR (€)	Aug. 30, 2025	Aug. 31, 2024	Jul. 30, 2024 EUR (€)
Debt Instrument [Line Items]
Kronos term loan from Contran | $						$ 53.7
Kronos Worldwide | Subordinated, unsecured term loan from Contran
Debt Instrument [Line Items]
Kronos term loan from Contran	$ 53.7	€ 50,000			$ 53.7
Interest rate								11.50%	9.54%
Interest rate spread			2.00%	2.00%
Kronos Worldwide | 9.50% Senior Secured Notes due 2029
Debt Instrument [Line Items]
Debt instrument principal amount | €		€ 276,174					€ 75,000			€ 75,000
Interest rate		9.50%			9.50%		9.50%			9.50%