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Plant, Equipment and Timberlands - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Accrued capital expenditures	$ 16.3glt_AccruedCapitalExpenditures	$ 11.9glt_AccruedCapitalExpenditures

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- Definition

Accrued Capital Expenditures

+ References

No definition available.

+ Details

Name:	glt_AccruedCapitalExpenditures
Namespace Prefix:	glt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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- Details

Name:	us-gaap_PropertyPlantAndEquipmentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration