Name:	fgbi_FinancingReceivableGrossCarryingAmountNetNonaccrual
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

Name:	fgbi_FinancingReceivablesFixedAndFloatingRateLoansByContractualMaturityAbstract
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Data Type:	xbrli:stringItemType
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Period Type:	duration

Financing receivables, excluding nonaccrual status notes, gross carrying amount that are maturing after fifteen years.

No definition available.

Name:	fgbi_FinancingReceivablesThatAreMaturingAfterFifteenYears
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financing receivables, excluding nonaccrual status notes, gross carrying amount that are maturing after five years but not more than fifteen years.

No definition available.

Name:	fgbi_FinancingReceivablesThatAreMaturingAfterFiveYearsButNotMoreThanFifteenYears
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financing receivables, excluding nonaccrual status notes, gross carrying amount that are maturing after one year but not more than five years.

No definition available.

Name:	fgbi_FinancingReceivablesThatAreMaturingAfterOneYearButNotMoreThanFiveYears
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financing receivables, excluding nonaccrual status notes, gross carrying amount that are maturing after one year or less.

No definition available.

Name:	fgbi_FinancingReceivablesThatAreMaturingAfterOneYearOrLess
Namespace Prefix:	fgbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of fee received for commitment to originate or purchase financing receivable where likelihood of commitment being exercised is remote, to be recognized as service income.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481598/310-20-45-2

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

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

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

Amortized cost excluding accrued interest, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

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

Amortized cost excluding accrued interest, of financing receivable on nonaccrual status. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16