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Debt - Activity (Details) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Oct. 01, 2024
Apr. 30, 2021
Debt Instrument [Line Items]        
Total debt $ 488.8 $ 528.2    
Industrial revenue bonds, variable        
Debt Instrument [Line Items]        
Maximum variable interest rate 12.00%      
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) $ 7.8 7.8    
Revolving credit facility | U.S. revolving credit facility        
Debt Instrument [Line Items]        
Revolving credit facility $ 19.6 20.0    
Stated interest rate, percentage 8.00%      
Revolving credit facility | Foreign line of credit        
Debt Instrument [Line Items]        
Revolving credit facility $ 0.0 34.0    
Stated interest rate, percentage 7.82%      
Casthouse Facility | Foreign line of credit        
Debt Instrument [Line Items]        
Revolving credit facility $ 9.0 9.0    
Financing fees 1.0      
Secured debt $ 108.7 114.2    
Stated interest rate, percentage 8.04%      
Vlissingen Credit Facility | Foreign line of credit        
Debt Instrument [Line Items]        
Secured debt $ 10.0 10.0    
Stated interest rate, percentage 7.98%   8.75%  
Senior secured notes, 7.5% | Senior notes        
Debt Instrument [Line Items]        
Financing fees $ 1.6      
Stated interest rate, percentage 7.50%     7.50%
7.5% senior secured notes due April 1, 2028, net of financing fees of $1.6 million at June 30, 2025, interest payable semiannually $ 248.4 248.1    
Senior convertible notes, 2.75% | Senior notes        
Debt Instrument [Line Items]        
Financing fees $ 1.0      
Stated interest rate, percentage 2.75%     2.75%
2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.0 million at June 30, 2025, interest payable semiannually $ 85.3 $ 85.1    
Industrial Revenue Bonds Due 2028        
Debt Instrument [Line Items]        
Stated interest rate, percentage 2.05%