Basis of Presentation - Basic and Diluted Earnings Per Common Share Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Basic earnings per common share calculation:
Net income applicable to FB Financial Corporation	$ 124,555	$ 190,285	$ 63,621
Dividends paid on and undistributed earnings allocated to participating securities	0	0	0
Earnings available to common shareholders	$ 124,555	$ 190,285	$ 63,621
Weighted average basic shares outstanding (in shares)	47,113,470	47,431,102	37,621,720
Basic earnings (loss) per common share (in dollars per share)	$ 2.64	$ 4.01	$ 1.69
Diluted earnings per common share:
Earnings available to common shareholders	$ 124,555	$ 190,285	$ 63,621
Weighted average basic shares outstanding (in shares)	47,113,470	47,431,102	37,621,720
Weighted average diluted shares contingently issuable (in shares)	126,321	524,778	478,024
Weighted average diluted shares outstanding (in shares)	47,239,791	47,955,880	38,099,744
Diluted (loss) earnings per common share (in dollars per share)	$ 2.64	$ 3.97	$ 1.67
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Restricted stock units outstanding considered to be antidilutive (in shares)	11,888	4,400	239,813