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Financial Derivatives and Hedging Activities - Additional Information (Detail) | 3 Months Ended
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Mar. 31, 2015
Designated as Hedging [Member] |
Derivative [Line Items] |
Production costs expected to be incurred maximum period | 12 months
Maximum maturity period of foreign currency derivative contracts designated as hedging instruments | 12 months
Not Designated as Hedging [Member] |
Derivative [Line Items] |
Maturities of foreign currency derivative contracts not designated as hedging instruments | 1 month
Fair Value, Measurements [Member] |
Derivative [Line Items] |
Accumulated other comprehensive income realization period | 12 months

X
- Definition Period over which deferred gains or losses are expected to be reclassed out of accumulated other comprehensive income. + References No definition available. + Details
Name: | glt_AccumulatedOtherComprehensiveIncomeRealizationPeriod
Namespace Prefix: | glt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maturities of foreign currency derivative contracts. + References No definition available. + Details
Name: | glt_MaturitiesOfForeignCurrencyDerivativeContracts
Namespace Prefix: | glt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The maximum duration of the derivative contract entered into to hedge foreign currency of expected production cost. + References No definition available. + Details
Name: | glt_MaximumMaturityPeriodOfForeignCurrencyDerivativeContracts
Namespace Prefix: | glt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period over which hedged production cost are expected to be incurred. + References No definition available. + Details
Name: | glt_ProductionCostsExpectedToBeIncurredMaximumPeriod
Namespace Prefix: | glt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |