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Income taxes - Additional Information (Details) - USD ($) $ in Thousands		9 Months Ended
	Jul. 18, 2025	Sep. 30, 2025	Sep. 30, 2024
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.		$ 5,283	$ 15,144
Foreign country
Income Tax Disclosure [Line Items]
Percentage of before current income tax expense (benefit)	15.00%
Percentage of reduction in enacted tax rate	1.00%
Percentage of after current income tax expense (benefit)	10.00%
Non-cash deferred income tax expense	$ 19,300

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) after change in the enacted rate.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) before change in the enacted rate.

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Percentage of reduction in enacted tax rate for each year.

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Income tax disclosure.

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Amount of deferred foreign income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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