XML 81 R71.htm IDEA: XBRL DOCUMENT
v3.25.1

EMPLOYEE BENEFIT PLANS - Narrative (Details) - Pension Plan - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2025 | Sep. 30, 2025
Defined Benefit Plan Disclosure [Line Items] |  |
Lump sum distribution for plan termination | $ 4,830 |
Subsequent Event | Forecast |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets, decrease for assets transferred from plan |  | $ 10,895

X
- Definition Defined Benefit Plan, Lump Sum Distribution For Plan Termination + References No definition available. + Details
Name: | gff_DefinedBenefitPlanLumpSumDistributionForPlanTermination
Namespace Prefix: | gff_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase (decrease) in plan assets of defined benefit plan from assets transferred into (from) plan. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanAssetsTransferredToFromPlan
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=gff_HunterFanPensionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |