Summary of significant accounting policies - Additional Information (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) a $ / shares	Dec. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($) $ / shares	Jul. 16, 2024	Jul. 15, 2024	Dec. 31, 2021 USD ($)
Summary of significant accounting policies
Deferred income tax liabilities	$ 57.7	$ 17.1
Retained earnings	574.7	475.8
Income tax expense (benefit)	$ 82.9	$ (24.6)	$ 36.8
Basic net loss per share | $ / shares	$ 3.79	$ (0.35)	$ 3.06
Diluted net loss per share | $ / shares	$ 3.79	$ (0.35)	$ 3.06
Net cash used in operating activities	$ 44.0	$ 3.9	$ 34.9
Net cash used in investing activities	(125.0)	(29.0)	(146.7)
Net cash used in financing activities	(2.3)	(75.9)	(114.0)
Capitalized interest costs on property and equipment	$ 1.0	1.9	1.7
Percentage of likelihood for recognition of uncertain tax positions	50.00%
Standard payment terms	less than one year
Shipping and handling costs	$ 1,680.3	1,676.5	1,732.1
Advertising costs	2.0	2.0	2.0
Research, development and certain sales technical support costs	14.0	18.0	16.0
Louisiana Pigment Company, L.P. (LPC)
Summary of significant accounting policies
Percentage owned manufacturing joint venture under equity method investment					50.00%
Revision of prior period, reclassification, adjustment
Summary of significant accounting policies
Deferred income tax liabilities		14.7	12.5
Restatement adjustment
Summary of significant accounting policies
Retained earnings						$ 15.5
Income tax expense (benefit)		$ 2.2	$ 3.0
Basic net loss per share | $ / shares		$ (0.07)	$ (0.10)
Diluted net loss per share | $ / shares		$ (0.07)	$ (0.10)
Net cash used in investing activities		$ 0.0	$ 0.0
Net cash used in financing activities		0.0	0.0
Chemicals
Summary of significant accounting policies
Shipping and handling costs	1,530.1	1,502.7	1,540.2
Shipping and Handling | Chemicals
Summary of significant accounting policies
Shipping and handling costs	$ 115.0	101.0	122.0
Residential or planned community
Summary of significant accounting policies
Area of real estate property | a	2,100
Residential Housing Unit | Minimum
Summary of significant accounting policies
Percentage of sales price	2.50%
Residential Housing Unit | Maximum
Summary of significant accounting policies
Percentage of sales price	3.50%
Kronos | Louisiana Pigment Company, L.P. (LPC)
Summary of significant accounting policies
Percentage held through wholly-owned subsidiary				50.00%	50.00%
Contran
Summary of significant accounting policies
Net cash payments received from/paid to tax group parent	$ 19.1	$ 14.2	$ 17.5
Contran | Valhi Incorporation
Summary of significant accounting policies
Parent company ownership interest	91.00%