Basis of Presentation - Schedule of Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Basic earnings per common share:
Net income applicable to FB Financial Corporation	$ 39,979	$ 35,299	$ 67,929	$ 71,680
Dividends paid on and undistributed earnings allocated to participating securities	0	0	0	0
Earnings available to common shareholders	$ 39,979	$ 35,299	$ 67,929	$ 71,680
Weighted average basic shares outstanding (in shares)	46,762,488	46,779,388	46,818,685	46,729,778
Basic earnings per common share (in dollars per share)	$ 0.85	$ 0.75	$ 1.45	$ 1.53
Diluted earnings per common share:
Earnings available to common shareholders	$ 39,979	$ 35,299	$ 67,929	$ 71,680
Weighted average basic shares outstanding (in shares)	46,762,488	46,779,388	46,818,685	46,729,778
Weighted average diluted shares contingently issuable (in shares)	82,655	35,466	92,781	47,825
Weighted average diluted shares outstanding (in shares)	46,845,143	46,814,854	46,911,466	46,777,603
Diluted earnings per common share (in dollars per share)	$ 0.85	$ 0.75	$ 1.45	$ 1.53
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	36,507	315,989	2,412	250,074