Basis of Presentation and Summary of Significant Accounting Polices - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Nov. 07, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Mar. 11, 2024	Dec. 31, 2023	Dec. 31, 2022
Restricted Cash and Cash Equivalents Items [Line Items]
Operating income (loss)		$ (25.2)	$ (44.0)	$ (96.3)	$ (125.9)
Net cash used in operating activities				(92.5)	$ (89.3)
Restricted cash		9.9		9.9			$ 9.7
Glencore Convertible Notes
Restricted Cash and Cash Equivalents Items [Line Items]
Amount Issued		306.2		306.2
Glencore Convertible Notes | Convertible Debt
Restricted Cash and Cash Equivalents Items [Line Items]
Amount Issued		300.3		300.3		$ 75.0	$ 225.3	$ 208.1
Subsequent Event
Restricted Cash and Cash Equivalents Items [Line Items]
Sale of stock, consideration received on transaction	$ 315.5
Subsequent Event | DOE Loan Facility | Line of Credit
Restricted Cash and Cash Equivalents Items [Line Items]
Amount Issued	475.0
Line of credit facility, maximum borrowing capacity	445.0
Line of credit facility, maximum capitalized interest	$ 30.0
Waste Disposal Obligation Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash		3.0		3.0
Bank Guarantee
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash		5.6		5.6
Cash Collateral
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash		$ 1.3		$ 1.3