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, 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

Debt Instrument, Increase (Decrease) In Borrowing Margin, Percentage

+ References

No definition available.

+ Details

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

- 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

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

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ 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:	glt_DebtCovenantPeriodAxis=glt_ThroughThePeriodEndedDecember312023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	glt_DebtCovenantPeriodAxis=glt_AfterThePeriodEndedDecember312023Member
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:

Long-Term Debt - Narrative (Detail)		6 Months Ended
Long-Term Debt - Narrative (Detail)	May 09, 2022	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 02, 2021 USD ($)	Sep. 02, 2021 EUR (€)
Debt Instrument [Line Items]
Letters of credit outstanding		$ 0
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 400,000,000
Percentage increase (decrease) in borrowing margin	0.25%
Debt instrument covenant compliance leverage ratio, actual		5.3
Revolving Credit Facility \| Through The Period Ended December 31, 2023
Debt Instrument [Line Items]
Debt instrument, covenant, net debt to EBITDA ratio, maximum	6.75
Revolving Credit Facility \| After The Period Ended December 31, 2023
Debt Instrument [Line Items]
Debt instrument, covenant, net debt to EBITDA ratio, maximum	4.0
Term Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity \| €					€ 220,000,000
Letters of Credit
Debt Instrument [Line Items]
Letters of credit issued		$ 6,700,000	$ 6,700,000