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Retirement Plans and Other Post-Retirement Benefits - Schedule of Target Allocation for Plan Assets (Detail) | 12 Months Ended
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Dec. 31, 2014
Large Cap [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Target allocation for the plan assets | 35.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = glt_LargeCapMember
Small and Mid Cap [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Target allocation for the plan assets | 12.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = glt_SmallAndMidCapMember
International Equity [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Target allocation for the plan assets | 13.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = glt_InternationalEquityMember
Real Estate Investment Trusts (REIT) [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Target allocation for the plan assets | 5.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = glt_RealEstateInvestmentTrustsMember
Fixed Income, Cash and Cash Equivalents [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Target allocation for the plan assets | 35.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = glt_FixedIncomeFundsAndCashAndCashEquivalentsMember

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- Definition Target allocation of investments of this type to total plan assets presented on a weighted average basis. + 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 (d)(i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920 + Details
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