Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Total principal amount of loans repurchased or indemnified	$ 1,137	$ 1,722	$ 2,907	$ 5,167

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