Fair Value of Financial Instruments (Detail) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Oct. 25, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 844,232,000	$ 775,941,000
Fair Value	640,188,000	792,906,000
Revolving credit facility, due Sep. 2026
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	118,685,000	10,000,000
Fair Value	$ 118,685,000	10,000,000
4.750% Senior Notes, due Oct. 2029
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	4.75%		4.75%
Carrying Value	$ 500,000,000	500,000,000	$ 500,000,000
Fair Value	301,250,000	516,875,000
Term loan, due Feb 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	193,588,000	218,026,000
Fair Value	$ 188,998,000	218,026,000
2.40% Term Loan, due Jun 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	2.40%
Carrying Value	$ 0	809,000
Fair Value	$ 0	813,000
2.05% Term Loan, due Mar 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	2.05%
Carrying Value	$ 1,423,000	7,556,000
Fair Value	$ 1,418,000	7,616,000
1.30% Term Loan, due Jun 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	1.30%
Carrying Value	$ 762,000	2,427,000
Fair Value	$ 754,000	2,433,000
1.55% Term Loan, due Sep 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	1.55%
Carrying Value	$ 3,594,000	5,204,000
Fair Value	$ 3,430,000	5,234,000
1.10% Term Loan, due Mar. 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	1.10%
Carrying Value	$ 4,848,000	9,267,000
Fair Value	$ 4,721,000	9,252,000
0.57% Term Loan, due Jul 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate on debt (as a percent)	0.57%
Carrying Value	$ 21,332,000	22,652,000
Fair Value	$ 20,932,000	$ 22,657,000

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

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

- Definition

Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI https://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

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(a)(16))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

Reference 5: 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 https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 7: 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 https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_RevolvingCreditFacilityDueSeptemberTwoThousandTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_FourPointSevenFiveSeniorNotesDueOctoberTwoThousandAndTwentyNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_TermLoanDueFebruaryTwoThousandAndTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_TwoPointFourZeroPercentTermLoanDueJuneTwoThousandTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_TwoPointZeroFivePercentTermLoanDueMarchTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_OnePointThreeZeroPercentageTermLoanDueJuneTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_OnePointFiveFivePercentageTermLoanDueSeptemberTwoThousandTwentyFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_OnePointOnePercentageTermLoanDueMarchTwoThousandTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=glt_PointFiveSevenPercentTermLoanDueJulyTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: