Other assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended						12 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Other Assets Non Current [Line Items]
Operating lease expense							$ 5.3	$ 5.2	$ 5.6
Operating lease, right-of-use asset			$ 2.8		$ 4.6		$ 1.8	$ 2.8	4.6
Weighted average remaining lease term			14 years				14 years	14 years
Weighted average discount rate associated with leases			6.00%				6.00%	6.00%
Operating lease not yet commenced, description							At December 31, 2025, we have no significant lease commitments that have not yet commenced.
Infrastructure reimbursement							$ 34.6	$ 31.7	25.5
Additional term for redevelopment plan							15 years
Operating lease liability							$ 19.9
City Of Henderson
Other Assets Non Current [Line Items]
Annual interest rate							6.00%
OPA | City of Henderson Redevelopment Agency
Other Assets Non Current [Line Items]
Tax increment reimbursement percentage							75.00%
Revenue from infrastructure reimbursement							$ 170.0
Revenue from interest income							39.0
OPA | City of Henderson Redevelopment Agency | Other income
Other Assets Non Current [Line Items]
Infrastructure reimbursement	$ 17.0	$ 17.2	$ 16.1	$ 14.2	$ 20.4	$ 4.8	34.2	$ 30.3	$ 25.2
OPA | Maximum | City of Henderson Redevelopment Agency
Other Assets Non Current [Line Items]
Reimbursement revenue							$ 209.0
Leverkusen TiO2 production facility
Other Assets Non Current [Line Items]
Percentage of production capacity							28.00%
Leverkusen TiO2 production facility | Chemicals
Other Assets Non Current [Line Items]
Operating lease liability							$ 7.6