Minimum Capital Requirements - Schedule of Actual and Required Capital Amounts and Ratios (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
FB Financial Corporation
Total Capital (to risk-weighted assets)
Actual, Amount	$ 1,608,166	$ 1,528,344
Actual, Ratio	0.141	0.131
Minimum Capital adequacy with capital buffer, Amount	$ 1,197,701	$ 1,225,161
Minimum Capital adequacy with capital buffer, Ratio	0.105	0.105
Tier 1 Capital (to risk-weighted assets)
Actual, Amount	$ 1,380,228	$ 1,315,386
Actual, Ratio	0.121	0.113
Minimum Capital adequacy with capital buffer, Amount	$ 969,568	$ 991,797
Minimum Capital adequacy with capital buffer, Ratio	8.50%	8.50%
Tier 1 Capital (to average assets)
Actual, Amount	$ 1,380,228	$ 1,315,386
Actual, Ratio	0.110	0.105
Minimum Capital adequacy with capital buffer, Amount	$ 500,573	$ 499,648
Minimum Capital adequacy with capital buffer. Ratio	0.040	0.040
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, Amount	$ 1,350,228	$ 1,285,386
Actual Ratio	11.80%	11.00%
Minimum Capital adequacy with capital buffer, Amount	$ 798,468	$ 816,774
Minimum Capital adequacy with capital buffer, Ratio	0.070	0.070
FirstBank
Total Capital (to risk-weighted assets)
Actual, Amount	$ 1,574,078	$ 1,506,543
Actual, Ratio	0.138	0.129
Minimum Capital adequacy with capital buffer, Amount	$ 1,195,510	$ 1,222,922
Minimum Capital adequacy with capital buffer, Ratio	0.105	0.105
To be well capitalized under prompt corrective action provisions, Amount	$ 1,138,581	$ 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	$ 1,346,139	$ 1,293,585
Actual, Ratio	0.118	0.111
Minimum Capital adequacy with capital buffer, Amount	$ 967,793	$ 989,985
Minimum Capital adequacy with capital buffer, Ratio	8.50%	8.50%
To be well capitalized under prompt corrective action provisions, Amount	$ 910,864	$ 931,750
To be well capitalized under prompt corrective action provisions, Ratio	0.080	0.080
Tier 1 Capital (to average assets)
Actual, Amount	$ 1,346,139	$ 1,293,585
Actual, Ratio	0.108	0.104
Minimum Capital adequacy with capital buffer, Amount	$ 499,962	$ 499,194
Minimum Capital adequacy with capital buffer. Ratio	0.040	0.040
To be well capitalized under prompt corrective action provisions, Amount	$ 624,952	$ 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	$ 1,346,139	$ 1,293,585
Actual Ratio	11.80%	11.10%
Minimum Capital adequacy with capital buffer, Amount	$ 797,006	$ 815,281
Minimum Capital adequacy with capital buffer, Ratio	0.070	0.070
To be well capitalized under prompt corrective action provisions, Amount	$ 740,077	$ 757,047
To be well capitalized under prompt corrective action provisions, Ratio	6.50%	6.50%