Basis of Presentation - Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Basic earnings per common share:
Net income applicable to FB Financial Corporation	$ 35,299	$ 19,345	$ 71,680	$ 54,581
Dividends paid on and undistributed earnings allocated to participating securities	0	0	0	0
Earnings available to common shareholders	$ 35,299	$ 19,345	$ 71,680	$ 54,581
Weighted average basic shares outstanding (in shares)	46,779,388	47,111,055	46,729,778	47,320,784
Basic earnings (loss) per common share (in dollars per share)	$ 0.75	$ 0.41	$ 1.53	$ 1.15
Diluted earnings per common share:
Earnings available to common shareholders	$ 35,299	$ 19,345	$ 71,680	$ 54,581
Weighted average basic shares outstanding (in shares)	46,779,388	47,111,055	46,729,778	47,320,784
Weighted average diluted shares contingently issuable (in shares)	35,466	100,595	47,825	145,507
Weighted average diluted shares outstanding (in shares)	46,814,854	47,211,650	46,777,603	47,466,291
Diluted (loss) earnings per common share (in dollars per share)	$ 0.75	$ 0.41	$ 1.53	$ 1.15
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	315,989	202,661	250,074	10,678