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Revenue, Contract Assets and Liabilities and Other Contract Matters - Additional Information (Details) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 USD ($) | Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) Vechicle
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Reduction of estimated contract price for liquidated damages, amount | $ 0.9 |  | $ 0.6
Towing, Salvage and Rescue Ship |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins | 8.4 |  |
Approved change order from increased contract price | 9.2 |  |
Increased craft labor costs | 0.8 |  |
Contractual obligation | 13.1 |  |
Gross profit recognized | 9.2 |  |
Payment received from change order | $ 8.8 |  |
Towing, Salvage and Rescue Ship | Minimum |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Projects, percent complete (percentage) | 15.00% |  |
Towing, Salvage and Rescue Ship | Maximum |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Projects, percent complete (percentage) | 65.00% |  |
Seventy-Vehicle Ferry |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins | $ 0.7 |  |
Projects, percent complete (percentage) | 65.00% |  |
Reserve for loss | $ 0.6 |  |
Offshore Facility Modules |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins | 0.6 |  |
Forty-Vehicle Ferry |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins |  |  | $ 1.2
Number of vehicle ferry projects | Vechicle |  |  | 2
Paddlewheel Riverboat and Subsea Components Projects |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins |  |  | $ 0.9
Shipyard |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins | 7.7 | $ 1.2 |
F&S |  |  |
Long Term Contracts Or Programs Disclosure [Line Items] |  |  |
Change in estimated margins | $ 0.6 | $ 0.9 |

X
- Definition Contract with customer asset cumulative catch-up adjustment to revenue approved change order. + References No definition available. + Details
Name: | gifi_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueApprovedChangeOrder
Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Contract with customer, asset, cumulative catch-up adjustment to revenue, change in estimated margins. + References No definition available. + Details
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Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Contract with customer asset cumulative catch-up adjustment to revenue increased craft labor costs. + References No definition available. + Details
Name: | gifi_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueIncreasedCraftLaborCosts
Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Contract With Customer, Reserve For Loss. + References No definition available. + Details
Name: | gifi_ContractWithCustomerReserveForLoss
Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Gross profit recognized due to cumulative effect impact from projects. + References No definition available. + Details
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Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Long-term Contracts or Programs Disclosure [Line Items] + References No definition available. + Details
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Namespace Prefix: | gifi_
Data Type: | xbrli:stringItemType
Balance Type: | na
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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 Projects, Percent Complete + References No definition available. + Details
Name: | gifi_ProjectsPercentComplete
Namespace Prefix: | gifi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Revenue variable consideration contract price reduction. + References No definition available. + Details
Name: | gifi_RevenueVariableConsiderationContractPriceReduction
Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Transaction price received from change order. + References No definition available. + Details
Name: | gifi_TransactionPriceReceivedFromChangeOrder
Namespace Prefix: | gifi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. + References No definition available. + Details
Name: | us-gaap_ContractualObligation
Namespace Prefix: | us-gaap_
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Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
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Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=gifi_ShipyardSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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