Financing Receivable, Collateral Dependent Loans, Amortized Cost

No definition available.

Name:	fbk_FinancingReceivableCollateralDependentLoansAmortizedCost
Namespace Prefix:	fbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percent Of Principal Balance Allowed To Buy Back Under Government National Mortgage Association Optional Repurchase Programs

+ References

No definition available.

+ Details

Name:	fbk_PercentOfPrincipalBalanceAllowedToBuyBackUnderGovernmentNationalMortgageAssociationOptionalRepurchasePrograms
Namespace Prefix:	fbk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of principal due on delinquent mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column H
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column H))
-URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014

+ Details

Name:	srt_MortgageLoansOnRealEstatePrincipalAmountOfDelinquentLoans
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123596393&loc=d3e14172-108612

+ Details

Name:	us-gaap_FairValueOptionChangesInFairValueGainLoss1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percent of remaining principal allowed to buy back under GNMA optional repurchase programs	100.00%
Mortgage Loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net (losses) gains from fair value changes of mortgage loans held for sale recorded in income	$ (16,874)	$ (20,716)
GNMA
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Delinquent GNMA loans that had been previously sold	70,672		$ 94,648
Level 3 \| Non-recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Amortized costs of collateral dependent loans	$ 5,034		$ 5,781