XML 90 R73.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Financial Derivatives and Hedging Activities - Additional Information (Detail) | 9 Months Ended
--- | ---
Sep. 30, 2018
Maximum [Member] | Fair Value, Measurements [Member] |
Derivative [Line Items] |
Accumulated other comprehensive income realization period | 18 months
Minimum [Member] | Fair Value, Measurements [Member] |
Derivative [Line Items] |
Accumulated other comprehensive income realization period | 12 months
Designated as Hedging [Member] | Cash Flow Hedges [Member] | Maximum [Member] |
Derivative [Line Items] |
Maturities of foreign currency derivative contracts | 18 months
Designated as Hedging [Member] | Cash Flow Hedges [Member] | Minimum [Member] |
Derivative [Line Items] |
Maturities of foreign currency derivative contracts | 1 month
Not Designated as Hedging [Member] |
Derivative [Line Items] |
Maturities of foreign currency derivative contracts | 1 month

X
- Definition Period over which deferred gains or losses are expected to be reclassified 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 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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
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_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
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: |