Organization and basis of presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Organization and basis of presentation [Line Items]
Deferred income taxes	$ 13.0		$ 13.0		$ 17.1
Retained earnings	499.0		499.0		475.8
Income tax expense (benefit)	$ 7.9	$ (6.8)	$ 12.3	$ (12.0)
Basic net loss per share	$ 0.70	$ (0.11)	$ 0.97	$ (0.31)
Diluted net loss per share	$ 0.70	$ (0.11)	$ 0.97	$ (0.31)
Restatement adjustment
Organization and basis of presentation [Line Items]
Deferred income taxes					$ (14.7)
Retained earnings		$ 13.5		$ 13.5		$ 11.6	$ 12.5
Income tax expense (benefit)		$ 1.9		$ 1.0
Basic net loss per share		$ (0.07)		$ (0.04)
Diluted net loss per share		$ (0.07)		$ (0.04)
Contran | Valhi Incorporation
Organization and basis of presentation [Line Items]
Parent company ownership interest	91.00%		91.00%