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Accounting Policies - Schedule of Range of Estimated Service Lives (Detail) | 12 Months Ended
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Dec. 31, 2014
Minimum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 5 years
Maximum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 30 years
Buildings [Member] | Minimum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 15 years
Buildings [Member] | Maximum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 45 years
Machinery and Equipment [Member] | Minimum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 5 years
Machinery and Equipment [Member] | Maximum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 40 years
Other [Member] | Minimum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 3 years
Other [Member] | Maximum [Member] |
Property Plant And Equipment Useful Life [Abstract] |
Range of estimated service lives | 25 years

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- Details
Name: | glt_PropertyPlantAndEquipmentUsefulLifeAbstract
Namespace Prefix: | glt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
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Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |