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Share-Based Compensation (Liability Classified Awards Narrative) (Details)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
Installment
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Restricted Stock Units Settled in Cash      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted (shares) | shares 263,998 147,851 98,364
Number of annual installment in which stock option exercisable | Installment 3    
Period from grant date for annual installment (in years) 1 year    
Granted (in USD per share) | $ / shares $ 6.04 $ 9.66 $ 10.71
Closing price (USD per share) | $ / shares $ 4.35    
Cash Incentive Award      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of annual installment in which stock option exercisable | Installment 3    
Cash Incentive Award | Suncoke LTCIP      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date fair value award | $ $ 2.0 $ 0.6 $ 1.0
Percent of award allocation 50.00%    
Measurement period 3 years