Mortgage Servicing Rights - Additional Information (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Transfers And Servicing [Abstract]
Mortgage loans serviced related to bulk sale of mortgage servicing rights	$ 0	$ 0

Mortgage loans serviced relates to sale of mortgage servicing rights.

No definition available.

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