Income taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2017
Income Tax [Line Items]
Deferred tax assets valuation allowance	$ 6.4	$ 3.8
Term of operating loss carryforwards	20 years
Business interest income, adjusted taxable income	30.00%
Deferred tax assets carryforwards related to nondeductible portion of interest expense	$ 3.5	0.9
Transition tax				$ 74.5
Income tax liability payable period	8 years
Noncurrent payable to affiliates	$ 18.6	33.5
Current payables to affiliates	31.3	22.9
Unrecognized tax benefits that would impact effective tax rate	2.8
Non-cash deferred income tax benefit	35.6	(1.6)	$ (11.0)
Non-cash deferred income tax expense	2.6
Related party
Income Tax [Line Items]
Noncurrent payable to affiliates	18.6	33.5
Current payables to affiliates	31.3	$ 22.9
Related party | Valhi
Income Tax [Line Items]
Noncurrent payable to affiliates	18.6
Current payables to affiliates	14.9
Payable to affiliate	33.5
Germany | Corporate Purposes
Income Tax [Line Items]
Net operating loss carryforwards	478.7
Deferred tax assets, operating loss carryforwards	75.8
Germany | Trade tax purposes
Income Tax [Line Items]
Net operating loss carryforwards	54.5
Deferred tax assets, operating loss carryforwards	5.9
Belgium | Corporate Purposes
Income Tax [Line Items]
Net operating loss carryforwards	47.0
Deferred tax assets, operating loss carryforwards	11.8
Canada | Corporate Purposes
Income Tax [Line Items]
Net operating loss carryforwards	31.5
Deferred tax assets, operating loss carryforwards	4.7
Canada | Provincial tax purposes
Income Tax [Line Items]
Net operating loss carryforwards	34.9
Deferred tax assets, operating loss carryforwards	$ 4.0