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Retirement Plans and Other Post-Retirement Benefits - Benefit Payments Expected to be Made under Non-Qualified Pension Plans and Other Benefit Plans (Detail) $ in Thousands | Dec. 31, 2018 USD ($)
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Nonqualified Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Benefit payments expected | $ 2,126
Other Benefit Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Benefit payments expected | $ 2,364

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- Definition Defined benefits plan expected benefit payments. + References No definition available. + Details
Name: | glt_DefinedBenefitsPlanExpectedBenefitPayments
Namespace Prefix: | glt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=glt_NonQualifiedPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=glt_OtherDefinedBenefitPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |