Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Total principal amount of loans repurchased or indemnified	$ 921	$ 1,418	$ 1,770	$ 3,445

Principal amount of loans repurchased or indemnified during period.

No definition available.

Name:	fbk_PrincipalAmountOfLoansRepurchasedOrIndemnifiedDuringPeriod
Namespace Prefix:	fbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration