Amount of letters of credit issued and reducing availability under revolving credit facility.

No definition available.

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

- Definition

Debt instrument covenant compliance leverage ratio actual.

+ References

No definition available.

+ Details

Name:	glt_DebtInstrumentCovenantComplianceLeverageRatioActual
Namespace Prefix:	glt_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument covenant compliance leverage ratio threshold.

+ References

No definition available.

+ Details

Name:	glt_DebtInstrumentCovenantComplianceLeverageRatioThreshold
Namespace Prefix:	glt_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Covenant Compliance, Leverage Ratio Threshold Following Material Acquisition

+ References

No definition available.

+ Details

Name:	glt_DebtInstrumentCovenantComplianceLeverageRatioThresholdFollowingMaterialAcquisition
Namespace Prefix:	glt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Covenant, Net Debt To EBITDA Ratio, Maximum

+ References

No definition available.

+ Details

Name:	glt_DebtInstrumentCovenantNetDebtToEBITDARatioMaximum
Namespace Prefix:	glt_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of Credit Facility, Accordion Feature, Increase Limit

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=glt_OvernightBankingFundingRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_EurodollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=glt_EuriborMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=glt_TermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=glt_SwingLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=glt_GeorgiaPacificMtHollyLLCGeorgiaPacificSUSNonwovensBusinessMountHollyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt - Narrative (Detail)	9 Months Ended
Long-Term Debt - Narrative (Detail)	Sep. 30, 2021 USD ($)	Oct. 29, 2023	Oct. 29, 2021	Sep. 02, 2021 USD ($)	Sep. 02, 2021 EUR (€)	May 13, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 01, 2019
Debt Instrument [Line Items]
Accordion feature				$ 150,000,000
Interest rate on debt								1.25%
Debt instrument covenant compliance leverage ratio, actual	2.6
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				400,000,000
Debt instrument covenant compliance leverage ratio, threshold	4.00
Debt instrument covenant compliance leverage ratio, threshold following a material acquisition	450.00%
Revolving Credit Facility \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument, covenant, net debt to EBITDA ratio, maximum			5.25
Revolving Credit Facility \| Subsequent Event \| Forecast
Debt Instrument [Line Items]
Debt instrument, covenant, net debt to EBITDA ratio, maximum		4.00
Revolving Credit Facility \| Minimum
Debt Instrument [Line Items]
Federal fund rate spread	0.125%
Revolving Credit Facility \| Maximum
Debt Instrument [Line Items]
Federal fund rate spread	1.00%
Revolving Credit Facility \| Overnight Banking Funding Rate
Debt Instrument [Line Items]
Federal fund rate spread	0.50%
Revolving Credit Facility \| Euro Rate
Debt Instrument [Line Items]
Federal fund rate spread	1.00%
Revolving Credit Facility \| EURIBOR \| Minimum
Debt Instrument [Line Items]
Federal fund rate spread	1.125%
Revolving Credit Facility \| EURIBOR \| Maximum
Debt Instrument [Line Items]
Federal fund rate spread	2.00%
Term Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity \| €					€ 220,000,000.0
Letters of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				30,000,000
Letters of credit issued	$ 6,700,000						$ 7,300,000
Letters of credit outstanding	$ 0
Swing Loans
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 30,000,000
Georgia-Pacific Mt. Holly LLC, Georgia-Pacific's U.S. Nonwovens Business ("Mount Holly")
Debt Instrument [Line Items]
Long-term line of credit						$ 160,000,000