Minimum Capital Requirements - Schedule of Actual and Required Capital Amounts and Ratios (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
FB Financial Corporation
Total Capital (to risk-weighted assets)
Actual, amount	$ 1,635,848	$ 1,528,344
Actual, Ratio	0.145	0.131
Minimum capital adequacy with capital buffer, amount	$ 1,182,028	$ 1,225,161
Minimum capital adequacy with capital buffer, ratio	0.105	0.105
Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,405,890	$ 1,315,386
Actual, ratio	0.125	0.113
Minimum capital adequacy with capital buffer, amount	$ 956,880	$ 991,797
Minimum capital adequacy with capital buffer, ratio	8.50%	8.50%
Tier 1 Capital (to average assets)
Actual, amount	$ 1,405,890	$ 1,315,386
Actual, Ratio	0.113	0.105
Minimum capital adequacy with capital buffer, amount	$ 496,485	$ 499,648
Minimum capital adequacy with capital buffer. ratio	0.040	0.040
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,375,890	$ 1,285,386
Actual ratio	12.20%	11.00%
Minimum capital adequacy with capital buffer, amount	$ 788,018	$ 816,774
Minimum capital adequacy with capital buffer, ratio	0.070	0.070
FirstBank
Total Capital (to risk-weighted assets)
Actual, amount	$ 1,600,950	$ 1,506,543
Actual, Ratio	0.142	0.129
Minimum capital adequacy with capital buffer, amount	$ 1,179,886	$ 1,222,922
Minimum capital adequacy with capital buffer, ratio	0.105	0.105
To be well capitalized under prompt corrective action provisions, Amount	$ 1,123,701	$ 1,164,688
To be well capitalized under prompt corrective action provisions, Ratio	0.100	0.100
Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,370,991	$ 1,293,585
Actual, ratio	0.122	0.111
Minimum capital adequacy with capital buffer, amount	$ 955,145	$ 989,985
Minimum capital adequacy with capital buffer, ratio	8.50%	8.50%
To be well capitalized under prompt corrective action provisions, Amount	$ 898,960	$ 931,750
To be well capitalized under prompt corrective action provisions, ratio	0.080	0.080
Tier 1 Capital (to average assets)
Actual, amount	$ 1,370,991	$ 1,293,585
Actual, Ratio	0.111	0.104
Minimum capital adequacy with capital buffer, amount	$ 495,761	$ 499,194
Minimum capital adequacy with capital buffer. ratio	0.040	0.040
To be well capitalized under prompt corrective action provisions, amount	$ 619,701	$ 623,992
To be well capitalized under prompt corrective action provisions, ratio	0.050	0.050
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,370,991	$ 1,293,585
Actual ratio	12.20%	11.10%
Minimum capital adequacy with capital buffer, amount	$ 786,590	$ 815,281
Minimum capital adequacy with capital buffer, ratio	0.070	0.070
To be well capitalized under prompt corrective action provisions, amount	$ 730,405	$ 757,047
To be well capitalized under prompt corrective action provisions, ratio	6.50%	6.50%