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Retirement Plans And Postretirement Benefits (Narrative) (Details) - USD ($)
 9 Months Ended 12 Months Ended
Jan. 25, 1995
Feb. 25, 1991
Sep. 30, 2018
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]            
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent   6.00%        
Defined benefit plan, accumulated benefit obligation       $ 176,300,000 $ 162,600,000  
Employee basic contribution percent       5.00%    
Employee supplemental contribution percent       45.00%    
Pension and other postretirement benefit contributions     $ 1,300,000 $ 2,200,000 2,100,000  
Union Carbide | GrafTech International Ltd [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions 50.00%          
Postemployment Retirement Benefit            
Defined Benefit Plan Disclosure [Line Items]            
Employer contributions       1,300,000 1,700,000  
Defined Benefit Plan, Benefit Obligation       17,200,000 18,100,000  
Net Cost       $ 700,000 $ 1,600,000 $ 0