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Business And Summary Of Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
Apr. 23, 2018
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Depreciation expense   $ 51,500,000 $ 49,700,000 $ 53,500,000  
Capital expenses included in accounts payable   8,900,000 11,500,000    
Deferred costs   18,100,000 20,200,000    
Amortized costs   9,200,000 4,100,000 3,500,000  
Related Party Tax Agreement Percent Of Savings 85.00%        
Environmental remediation, compliance and management expenses   11,100,000 11,600,000 12,400,000  
Accrued liability relating to environmental remediation   4,900,000 4,900,000    
Capitalized maintenance cost   10,200,000 800,000    
Amortization of deferred maintenance cost   6,000,000.0 5,100,000 3,100,000  
Stockholders' Equity Attributable to Parent   $ (329,385,000) (691,073,000) (1,076,769,000) $ 613,215,000
London Interbank Offered Rate (LIBOR) [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Due to Related Party, Basis Spread on Variable Rate 0.0100        
Interest rate swap          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Derivative, Term of Contract   2 years      
Interest rate swap 2          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Derivative, Term of Contract   5 years      
Minimum [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Revenue From Contract With Customer, Term Of Contract   1 year      
Maximum [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Revenue From Contract With Customer, Term Of Contract   5 years      
GrafTech International Ltd [Member] | Brookfield [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions   55.30%      
Retained Earnings [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Stockholders' Equity Attributable to Parent   $ (1,070,770,000) (1,451,836,000) $ (1,893,496,000) $ (261,411,000)
Cumulative Effect, Period of Adoption, Adjustment          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Stockholders' Equity Attributable to Parent     (2,026,000)    
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Stockholders' Equity Attributable to Parent     $ (2,026,000)