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Operating Segments - Summarized Segment Financial Information (Parenthetical) (Details) - Forty-Vehicle Ferry $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2019 USD ($) Vechicle | Sep. 30, 2020 Vechicle | Sep. 30, 2019 USD ($) Vechicle
Segment Reporting Information [Line Items] |  |  |
Revenue reclassified between the Shipyard and Fabrication & Services segments | $ | $ 3.9 |  | $ 7.2
Number of vehicle ferry projects | Vechicle | 2 | 2 | 2

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- Definition Number of vehicle ferry projects. + References No definition available. + Details
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Namespace Prefix: | gifi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Revenue reclassified between segments. + References No definition available. + Details
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Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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- Details
Name: | srt_ProductOrServiceAxis=gifi_FortyVehicleFerryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |