Accrued environmental loss contingencies remaining amount.

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- Definition

Anticipated cost to complete work for remaining site remedy.

+ References

No definition available.

+ Details

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- Definition

Commitments Contingencies And Litigation [Line Items]

+ References

No definition available.

+ Details

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- Definition

Contribution payment towards remedial action and natural resource damages.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Costs And Damages Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	glt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimated cost of cleanup work.

+ References

No definition available.

+ Details

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Namespace Prefix:	glt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expected cleanup work continuation period description.

+ References

No definition available.

+ Details

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

- Definition

Expected payments for governments unreimbursed past costs which are under dispute.

+ References

No definition available.

+ Details

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

- Definition

The specific areas of the site into which the contaminated area has been separated by the US EPA.

+ References

No definition available.

+ Details

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

- Definition

Period over which cash expenditure to be incurred.

+ References

No definition available.

+ Details

Name:	glt_PeriodOverWhichCashExpenditureToBeIncurred
Namespace Prefix:	glt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Settlement payable date.

+ References

No definition available.

+ Details

Name:	glt_SettlementPayableDate
Namespace Prefix:	glt_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
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-Section 50
-Paragraph 1
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (c),(d)(2)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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Balance Type:
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- Details

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Balance Type:
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- Details

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- Details

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- Details

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- Details

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Commitments, Contingencies and Legal Proceedings - Additional Information (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) Operable_Unit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitments Contingencies And Litigation [Line Items]
Number of operable units \| Operable_Unit	5
Reserve for Environmental liabilities, current portion	$ 29,500	$ 25,000
Other Long-Term Liabilities [Member]
Commitments Contingencies And Litigation [Line Items]
Reserve for Environmental liabilities, remaining portion	23,200
NCR/Appvion Consent Decree [Member]
Commitments Contingencies And Litigation [Line Items]
Contribution payment towards remedial action and natural resource damages	65,000
Anticipated cost to complete work for remaining site remedy	200,000
Expected payments for governments unreimbursed past costs which are under dispute	$ 34,000
Minimum [Member] \| December 2009 - Long Term Monitoring Plan [Member]
Commitments Contingencies And Litigation [Line Items]
Period over which cash expenditure to be incurred for monitoring activities	30 years
Maximum [Member]
Commitments Contingencies And Litigation [Line Items]
Estimated cost related to Fox River matter	$ 150,000
Maximum [Member] \| NCR/Appvion Consent Decree [Member]
Commitments Contingencies And Litigation [Line Items]
Estimated cost related to Fox River matter	30,000
Georgia Pacific [Member]
Commitments Contingencies And Litigation [Line Items]
Settlement payable amount	$ 9,500
Payment due date	2017-08
GLT, GP and NCR [Member] \| Minimum [Member] \| NCR/Appvion Consent Decree [Member]
Commitments Contingencies And Litigation [Line Items]
Contribution payment towards remedial action and natural resource damages	$ 1,000,000
OU2-5 [Member]
Commitments Contingencies And Litigation [Line Items]
Estimated future cost of cleanup work		$ 13,400	$ 13,400
Expected cleanup work continuation year	through 2018
NCR costs and damages percentage	100.00%
OU2-5 [Member] \| Whiting Litigation [Member]
Commitments Contingencies And Litigation [Line Items]
NCR costs and damages percentage	100.00%