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Retirement Plans And Postretirement Benefits (Net Postretirement Benefit Costs And Postretirement Projected Benefit Obligation) (Details) | 12 Months Ended
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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

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- Definition Defined Benefit Plan Year Rate Reached Ultimate Trend Rate. + References No definition available. + Details
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- Definition The interest rate used to adjust for the time value of money for the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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- Definition The interest rate used to adjust for the time value of money. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 + Details
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- Definition The ultimate trend rate for health care costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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