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Organization And Summary Of Significant Accounting Policies (Details)
$ / shares in Units, $ in Thousands
 6 Months Ended 12 Months Ended
Jul. 22, 2020
Jun. 30, 2020
USD ($)
Dec. 31, 2019
USD ($)
Mar. 31, 2020
USD ($)
Jun. 30, 2019
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Jun. 30, 2018
major_product_categories
Apr. 26, 2018
$ / shares
shares
Accounting Policies [Abstract]                  
Shares, Issued | shares                 38,097,525
Sale of Stock, Price Per Share | $ / shares                 $ 15.00
Number of major product categories | major_product_categories               2  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                  
Total stockholders' equity   $ 574,714 $ 691,073 $ 680,379 $ 709,838 $ 881,618 $ 1,076,769    
Accounting Standards Update [Extensible List]   us-gaap:AccountingStandardsUpdate201613Member us-gaap:AccountingStandardsUpdate201613Member            
GrafTech International Ltd | Brookfield                  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                  
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions   75.00%              
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions   75.00%              
GrafTech International Ltd | Brookfield | Subsequent Event                  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                  
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions 65.00%                
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions 65.00%                
Retained Earnings (Accumulated Deficit)                  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                  
Total stockholders' equity   $ 1,284,756 $ 1,451,836 $ 1,374,844 $ 1,549,082 $ 1,720,756 $ 1,893,496    
Cumulative Effect, Period of Adoption, Adjusted Balance                  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                  
Total stockholders' equity     2,026            
Cumulative Effect, Period of Adoption, Adjusted Balance | Retained Earnings (Accumulated Deficit)                  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                  
Total stockholders' equity     $ 2,026