Basis of Presentation - Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Basic earnings per common share calculation:
Net income applicable to FB Financial Corporation	$ 31,831	$ 45,290	$ 86,412	$ 141,458
Dividends paid on and undistributed earnings allocated to participating securities	0	0	0	0
Earnings available to common shareholders	$ 31,831	$ 45,290	$ 86,412	$ 141,458
Weighted average basic shares outstanding (in shares)	46,908,520	47,412,214	47,181,853	47,345,984
Basic earnings (loss) per common share (in dollars per share)	$ 0.68	$ 0.96	$ 1.83	$ 2.99
Diluted earnings per common share:
Earnings available to common shareholders	$ 31,831	$ 45,290	$ 86,412	$ 141,458
Weighted average basic shares outstanding (in shares)	46,908,520	47,412,214	47,181,853	47,345,984
Weighted average diluted shares contingently issuable (in shares)	116,091	594,933	133,247	637,510
Weighted average diluted shares outstanding (in shares)	47,024,611	48,007,147	47,315,100	47,983,494
Diluted (loss) earnings per common share (in dollars per share)	$ 0.68	$ 0.94	$ 1.83	$ 2.95
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	15,408	15,974	11,888	20,448