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Plant, Equipment and Timberlands - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Property Plant And Equipment Useful Life And Values [Abstract]
Accrued capital expenditures	$ 11.9	$ 21.7

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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:	glt_PropertyPlantAndEquipmentUsefulLifeAndValuesAbstract
Namespace Prefix:	glt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration