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CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION (Details) | 12 Months Ended
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Sep. 30, 2018
Clopay Ames True Temper Holding, Corp. [Member] |
Condensed Financial Statements, Captions [Line Items] |
Subsidiary percentage ownership | 100.00%
AMES Southern, Inc. [Member] |
Condensed Financial Statements, Captions [Line Items] |
Subsidiary percentage ownership | 100.00%
The AMES Companies, Inc. [Member] |
Condensed Financial Statements, Captions [Line Items] |
Subsidiary percentage ownership | 100.00%
Telephonics Corporation [Member] |
Condensed Financial Statements, Captions [Line Items] |
Subsidiary percentage ownership | 100.00%
Clopay Building Products [Member] |
Condensed Financial Statements, Captions [Line Items] |
Subsidiary percentage ownership | 100.00%

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- 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
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- Definition Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions. + References No definition available. + Details
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- Details
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Data Type: | na
Balance Type: |
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- Details
Name: | dei_LegalEntityAxis=gff_AMESSouthernInc.Member
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Data Type: | na
Balance Type: |
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- Details
Name: | dei_LegalEntityAxis=gff_TheAMESCompaniesInc.Member
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Period Type: |

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- Details
Name: | dei_LegalEntityAxis=gff_TelephonicsCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
Name: | dei_LegalEntityAxis=gff_ClopayBuildingProductsMember
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Balance Type: |
Period Type: |