Name:	fgbi_FinancingReceivableModificationsAdditions
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Reflects the amount of investment related to financing receivables constructed to permanent financing related to a troubled debt restructuring.

No definition available.

Name:	fgbi_FinancingReceivableModificationsConstructionToPermanentFinancing
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Reflects the amount of other adjustments of investment related to financing receivables that have been modified by troubled debt restructurings during the period.

No definition available.

Name:	fgbi_FinancingReceivableModificationsOtherAdjustments
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Reflects the amount of paydowns of investment related to financing receivables that have been modified by troubled debt restructurings during the period.

No definition available.

Name:	fgbi_FinancingReceivableModificationsPaydowns
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Reflects the amount of investment related to financing receivables restructured to market terms related to a troubled debt restructuring.

No definition available.

Name:	fgbi_FinancingReceivableModificationsRestructuredToMarketTerms
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Reflects the amount of the financial receivables related to a troubled debt restructuring, which were transferred to other real estate during the period.

No definition available.

Name:	fgbi_FinancingReceivableModificationsTransferredToOtherRealEstate
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

Name:	fgbi_TroubledDebtRestructuringActivityRollForward
Namespace Prefix:	fgbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Reflects the amount of the write-down related to a troubled debt restructuring.

Name:	us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_ConstructionAndLandDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_FarmlandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_OneToFourFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_Multi-FamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_NonFarmNonResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=fgbi_NonRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_AgriculturalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fgbi_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: