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Accounting Policies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2013
Accounting Policies [Abstract] |
Maturity period of cash and cash equivalents | Three months or less

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- Definition Maturity period of cash and cash equivalents. + References No definition available. + Details
Name: | glt_CashAndCashEquivalentsMaturityDescription
Namespace Prefix: | glt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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