Basis of Presentation - Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Basic earnings per common share:
Net income applicable to FB Financial Corporation	$ 36,381	$ 35,236
Dividends paid on and undistributed earnings allocated to participating securities	0	0
Earnings available to common shareholders	$ 36,381	$ 35,236
Weighted average basic shares outstanding (in shares)	46,679,618	47,530,520
Basic earnings (loss) per common share (in dollars per share)	$ 0.78	$ 0.74
Diluted earnings per common share:
Earnings available to common shareholders	$ 36,381	$ 35,236
Weighted average basic shares outstanding (in shares)	46,679,618	47,530,520
Weighted average diluted shares contingently issuable (in shares)	85,536	193,382
Weighted average diluted shares outstanding (in shares)	46,765,154	47,723,902
Diluted (loss) earnings per common share (in dollars per share)	$ 0.78	$ 0.74
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	159,946	123,709