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Retirement Plans And Postretirement Benefits (Net Postretirement Benefit Costs And Postretirement Projected Benefit Obligation) (Details)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Postretirement Benefit Obligations [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 4.82%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gti_PostRetirementBenefitObligationsMember
5.41%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gti_PostRetirementBenefitObligationsMember
Health care cost trend on covered charges, Initial 6.55%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gti_PostRetirementBenefitObligationsMember
7.42%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gti_PostRetirementBenefitObligationsMember
Health care cost trend on covered charges, Ultimate 6.18%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gti_PostRetirementBenefitObligationsMember
6.23%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= gti_PostRetirementBenefitObligationsMember
Health care cost trend on covered charges, Years to ultimate 1 year 3 years
Postretirement Benefit Costs [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 5.29%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PostretirementBenefitCostsMember
4.44%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PostretirementBenefitCostsMember
Health care cost trend on covered charges, Initial 7.39%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PostretirementBenefitCostsMember
7.52%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PostretirementBenefitCostsMember
Health care cost trend on covered charges, Ultimate 6.18%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PostretirementBenefitCostsMember
5.94%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PostretirementBenefitCostsMember
Health care cost trend on covered charges, Years to ultimate 2 years 3 years