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Retirement Plans and Other Post-Retirement Benefits - Schedule of Target Allocation for Plan Assets (Detail)	12 Months Ended
	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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- Details

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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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- Details

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- Details

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