Income taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.	$ 7,044	$ 16,905	$ 26,766
Gross unrecognized tax benefits	7,300	7,300	7,300
Uncertain tax position		4,778
Unrecognized tax benefits, if recognize which would affect effective tax rate	7,300
Deferred Tax Assets, Operating Loss Carryforwards	825
Currently payable	168	340	307
Deferred income tax expense	$ (16,221)	13,718	(7,308)
Income tax examination	We believe we have adequate accruals for additional taxes and related interest expense which could ultimately result from tax examinations. We believe the ultimate disposition of tax examinations should not have a material adverse effect on our consolidated financial position, results of operations or liquidity.
Federal Income Tax Purposes
Income Tax Disclosure [Line Items]
Net operating loss carryforwards expiration description	an indefinite carryforward period subject to an 80% annual usage limitation.
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	$ 800
Kronos
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.	$ 7,000	$ 16,900	$ 26,800