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Goodwill And Other Intangible Assets (Narrative) (Details) (USD $)
 3 Months Ended 12 Months Ended 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Jun. 30, 2015
Goodwill [Line Items]        
Goodwill, impairment loss $ 35,381,000us-gaap_GoodwillImpairmentLoss      
Amortization expense of intangible assets 4,300,000us-gaap_AmortizationOfIntangibleAssets 4,800,000us-gaap_AmortizationOfIntangibleAssets    
Estimated amortization expense, remainder of 2015 12,800,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear      
Estimated amortization expense, 2016 13,100,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo      
Estimated amortization expense, 2017 11,800,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree      
Estimated amortization expense, 2018 10,700,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour      
Estimated amortization expense, 2019 9,200,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive      
Needle Coke        
Goodwill [Line Items]        
Goodwill, impairment loss $ 35,400,000us-gaap_GoodwillImpairmentLoss
/ us-gaap_SubsegmentsAxis
= gti_NeedleCokeMember		   $ 75,700,000us-gaap_GoodwillImpairmentLoss
/ us-gaap_SubsegmentsAxis
= gti_NeedleCokeMember		  
Discounted cash flow model, period of forecasted cash flows 17 years      
Discounted cash flow model, discount rate 10.50%us-gaap_FairValueInputsDiscountRate
/ us-gaap_SubsegmentsAxis
= gti_NeedleCokeMember		      
Needle Coke | Scenario, Forecast        
Goodwill [Line Items]        
Decrease in market prices       18.00%gti_PercentageDecreaseinMarketPrices
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
/ us-gaap_SubsegmentsAxis
= gti_NeedleCokeMember