Basis of Presentation - Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Basic earnings per common share calculation:
Net income applicable to FB Financial Corporation	$ 35,236	$ 52,874
Dividends paid on and undistributed earnings allocated to participating securities	0	0
Earnings available to common shareholders	$ 35,236	$ 52,874
Weighted average basic shares outstanding (in shares)	47,530,520	47,278,865
Basic earnings (loss) per common share (in dollars per share)	$ 0.74	$ 1.12
Diluted earnings per common share:
Earnings available to common shareholders	$ 35,236	$ 52,874
Weighted average basic shares outstanding (in shares)	47,530,520	47,278,865
Weighted average diluted shares contingently issuable (in shares)	193,382	690,241
Weighted average diluted shares outstanding (in shares)	47,723,902	47,969,106
Diluted (loss) earnings per common share (in dollars per share)	$ 0.74	$ 1.10
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	123,709	87,452