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

The amount of travel expense incurred during the period on a debt or other obligation to a related party.

No definition available.

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

Refer to the amount of unfunded commitments for which the entity is obligated to.

No definition available.

Name:	fgbi_RelatedPartyUnfundedCommitments
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(e))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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

Reflects the sum for the period of the additions and reductions to related party loans, which when added to the opening balance of related party loan will agree to the ending balance of such loans. This subtotal typically is not reflected.

Name:	us-gaap_LoansAndLeasesReceivableRelatedPartiesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
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:	us-gaap_LoansAndLeasesReceivableRelatedPartiesRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Name:	us-gaap_RelatedPartyDepositLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864