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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Basic earnings per common share calculation:
Net income applicable to FB Financial Corporation	$ 19,345	$ 43,294	$ 54,581	$ 96,168
Dividends paid on and undistributed earnings allocated to participating securities	0	0	0	0
Earnings available to common shareholders	$ 19,345	$ 43,294	$ 54,581	$ 96,168
Weighted average basic shares outstanding (in shares)	47,111,055	47,351,969	47,320,784	47,312,312
Basic earnings (loss) per common share (in dollars per share)	$ 0.41	$ 0.91	$ 1.15	$ 2.03
Diluted earnings per common share:
Earnings available to common shareholders	$ 19,345	$ 43,294	$ 54,581	$ 96,168
Weighted average basic shares outstanding (in shares)	47,111,055	47,351,969	47,320,784	47,312,312
Weighted average diluted shares contingently issuable (in shares)	100,595	641,804	145,507	664,221
Weighted average diluted shares outstanding (in shares)	47,211,650	47,993,773	47,466,291	47,976,533
Diluted (loss) earnings per common share (in dollars per share)	$ 0.41	$ 0.90	$ 1.15	$ 2.00
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	202,661	164,472	10,678	250,776