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Customer Concentrations (Narrative) (Details)
T in Millions, $ in Millions
12 Months Ended
Dec. 31, 2022
USD ($)
customer
T
Dec. 31, 2021
USD ($)
Concentration Risk [Line Items]    
Number of primary customers | customer 2  
Customer Concentration Risk    
Concentration Risk [Line Items]    
Quantity of coke sold to three primary customers (in tons) | T 3.4  
Customer Concentration Risk | Cliffs Steel | Accounts Receivable    
Concentration Risk [Line Items]    
Accounts receivable net $ 33.5 $ 30.0
Customer Concentration Risk | U.S. Steel | Accounts Receivable    
Concentration Risk [Line Items]    
Accounts receivable net $ 7.1 $ 7.3
Customer Concentration Risk | Cliffs Steel and U.S. Steel | Accounts Receivable    
Concentration Risk [Line Items]    
Concentration risk, percentage 39.00% 48.00%