Income taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.		$ 16,905	$ 26,766	$ 26,766
Gross unrecognized tax benefits	$ 7,300	7,300	7,300	7,300
Unrecognized tax benefits, if recognize which would affect effective tax rate	7,300	7,300
Currently payable		340	307	495
Deferred income tax expense		13,718	(7,308)	2,291
Uncertain tax position	4,778	4,778	3,707
Federal Income Tax Purposes
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	2,500	$ 2,500
Net operating loss carryforwards expiration description		an indefinite carryforward period subject to an 80% annual usage limitation.
Kronos
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.		$ 16,900	26,800	$ 26,800
Deferred income tax asset valuation allowance			0
Deferred Tax Assets	13,300	13,300	$ 3,500
Non-cash deferred income tax expense		5,700
Unpaid transition tax payable	18,600	18,600
Pretransition gain	77,100
Deferred income tax expense	16,500
Kronos | German
Income Tax Disclosure [Line Items]
Deferred income tax asset valuation allowance	0	0
Kronos | Belgium
Income Tax Disclosure [Line Items]
Deferred income tax asset valuation allowance	8,200	8,200
Kronos | Canada
Income Tax Disclosure [Line Items]
Operating loss carryforwards expiration period			20 years
Deferred income tax asset valuation allowance	0	0
Kronos | Deferred Tax Liability Non Current
Income Tax Disclosure [Line Items]
Uncertain tax position	2,500	2,500
Kronos | Corporate Tax Purposes | German
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards	447,300	447,300
Deferred Tax Assets, Operating Loss Carryforwards	70,800	70,800
Kronos | Corporate Tax Purposes | Belgium
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards	72,000	72,000
Deferred Tax Assets, Operating Loss Carryforwards	18,000	18,000
Kronos | Corporate Tax Purposes | Canada
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards	28,900	28,900
Deferred Tax Assets, Operating Loss Carryforwards	4,300	4,300
Kronos | Trade Tax Purposes | German
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards	40,100	40,100
Deferred Tax Assets, Operating Loss Carryforwards	4,400	4,400
Kronos | Provincial Tax Purposes | Canada
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards	31,100	31,100
Deferred Tax Assets, Operating Loss Carryforwards	$ 3,600	$ 3,600
Kronos European Subsidiaries | Transition Tax
Income Tax Disclosure [Line Items]
Currently payable					$ 74,500
Current income tax expense payment period					8 years