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Goodwill and Intangible Assets (Details Textual) | 12 Months Ended
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Dec. 31, 2012
Goodwill and Intangible Assets (Textual) [Abstract] |
Remaining weighted average useful life of intangible assets | 8 years 2 months 12 days
Customer relationships [Member] | Maximum [Member] |
Finite-Lived Intangible Assets [Line Items] |
Finite-Lived Intangible Asset, Useful Life | 14 years
Customer relationships [Member] | Minimum [Member] |
Finite-Lived Intangible Assets [Line Items] |
Finite-Lived Intangible Asset, Useful Life | 3 years
Technology and related [Member] | Maximum [Member] |
Finite-Lived Intangible Assets [Line Items] |
Finite-Lived Intangible Asset, Useful Life | 20 years
Technology and related [Member] | Minimum [Member] |
Finite-Lived Intangible Assets [Line Items] |
Finite-Lived Intangible Asset, Useful Life | 14 years

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- Definition Finite lived intangible asset remaining amortization period. + References No definition available. + Details
Name: | glt_FiniteLivedIntangibleAssetRemainingAmortizationPeriod
Namespace Prefix: | glt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

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

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration