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Income Taxes - Summary of Tax Years that Remain Subject to Examination by Major Jurisdiction (Detail)	9 Months Ended
	Sep. 30, 2013
United States - Federal [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2010 - 2012
United States - State [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2008 -2012
Examination in progress	2009
Canada [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2010 - 2012
Examination in progress	2007 - 2011
Germany [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2012
Examination in progress	2007 - 2012
France [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2010 -2012
United Kingdom [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2009 - 2012
Philippines [Member]
Income Tax Examination [Line Items]
Examinations not yet initiated	2012
Examination in progress	2010-2011

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- Definition

Income tax examination in progress.

+ References

No definition available.

+ Details

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X

- Definition

Income tax examination not yet initiated.

+ References

No definition available.

+ Details

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

X

- Details

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