Other assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended						12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Other Assets Non Current [Line Items]
Operating lease expense							$ 5.2	$ 5.6	$ 5.5
Operating lease, right-of-use asset	$ 2.8		$ 4.6		$ 6.6		$ 2.8	$ 4.6	6.6
Weighted average remaining lease term	14 years		14 years				14 years	14 years
Weighted average discount rate associated with leases	6.00%		5.00%				6.00%	5.00%
Operating lease not yet commenced, description							At December 31, 2024, we have no significant lease commitments that have not yet commenced.
Infrastructure reimbursement							$ 31.7	$ 25.5	16.0
Additional term for redevelopment plan										15 years
Operating lease liability	$ 20.6						$ 20.6
City of Henderson Redevelopment Agency | Tax Increment Reimbursement, Quarter Three
Other Assets Non Current [Line Items]
Infrastructure reimbursement		$ 14.2		$ 4.8		$ 10.0
City of Henderson Redevelopment Agency | Tax Increment Reimbursement, Quarter Four
Other Assets Non Current [Line Items]
Infrastructure reimbursement	16.1		$ 20.4		$ 5.2
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%
OPA | City of Henderson Redevelopment Agency | OtherIncome
Other Assets Non Current [Line Items]
Infrastructure reimbursement							$ 30.3	$ 25.2	$ 15.2
OPA | Maximum | City of Henderson Redevelopment Agency
Other Assets Non Current [Line Items]
Reimbursement revenue	209.0						209.0
Leverkusen TiO2 production facility | Chemicals
Other Assets Non Current [Line Items]
Operating lease liability	$ 6.8						$ 6.8