Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Total principal amount of loans repurchased or indemnified	$ 1,119	$ 849

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