XML 89 R73.htm IDEA: XBRL DOCUMENT
v3.21.2

Leases - Narrative (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | May 13, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Operating Leased Assets [Line Items] |  |  |
Right of use asset | $ 22,513 |  | $ 11,789
Mount Holly Acquisition |  |  |
Operating Leased Assets [Line Items] |  |  |
Right of use asset |  | $ 7,700 |

X
- Definition Amount of lessee's right to use underlying asset under operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
Name: | us-gaap_OperatingLeaseRightOfUseAsset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=glt_MountHollyAcquisitionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |