Minimum Capital Requirements - Schedule of Actual and Required Capital Amounts and Ratios (Details) $ in Thousands	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
FB Financial Corporation
Total Capital (to risk-weighted assets)
Actual, amount	$ 1,686,651	$ 1,635,848
Actual, ratio	0.151	0.145
Minimum requirement for capital adequacy with capital buffer, amount	$ 1,170,701	$ 1,182,028
Minimum requirement for capital adequacy with capital buffer, ratio	0.105	0.105
Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,447,410	$ 1,405,890
Actual, ratio	0.130	0.125
Minimum requirement for capital adequacy with capital buffer, amount	$ 947,711	$ 956,880
Minimum requirement for capital adequacy with capital buffer, ratio	0.085	0.085
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,417,410	$ 1,375,890
Actual ratio	0.127	0.122
Minimum requirement for capital adequacy with capital buffer, amount	$ 780,468	$ 788,018
Minimum requirement for capital adequacy with capital buffer, ratio	0.070	0.070
Tier 1 Capital (to average assets)
Actual, amount	$ 1,447,410	$ 1,405,890
Actual, ratio	0.115	0.113
Minimum requirement for capital adequacy with capital buffer, amount	$ 505,439	$ 496,485
Minimum requirement for capital adequacy with capital buffer, ratio	0.040	0.040
FirstBank
Total Capital (to risk-weighted assets)
Actual, amount	$ 1,651,199	$ 1,600,950
Actual, ratio	0.149	0.142
Minimum requirement for capital adequacy with capital buffer, amount	$ 1,167,269	$ 1,179,886
Minimum requirement for capital adequacy with capital buffer, ratio	0.105	0.105
To qualify as well-capitalized under prompt corrective action provision, amount	$ 1,111,684	$ 1,123,701
To qualify as well-capitalized under prompt corrective action provision, ratio	0.100	0.100
Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,412,362	$ 1,370,991
Actual, ratio	0.127	0.122
Minimum requirement for capital adequacy with capital buffer, amount	$ 944,932	$ 955,145
Minimum requirement for capital adequacy with capital buffer, ratio	0.085	0.085
To qualify as well-capitalized under prompt corrective action provision, amount	$ 889,347	$ 898,960
To qualify as well-capitalized under prompt corrective action provision, ratio	0.080	0.080
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,412,362	$ 1,370,991
Actual ratio	0.127	0.122
Minimum requirement for capital adequacy with capital buffer, amount	$ 778,179	$ 786,590
Minimum requirement for capital adequacy with capital buffer, ratio	0.070	0.070
To qualify as well-capitalized under prompt corrective action provision, amount	$ 722,595	$ 730,405
To qualify as well-capitalized under prompt corrective action provision, ratio	0.065	0.065
Tier 1 Capital (to average assets)
Actual, amount	$ 1,412,362	$ 1,370,991
Actual, ratio	0.112	0.111
Minimum requirement for capital adequacy with capital buffer, amount	$ 504,643	$ 495,761
Minimum requirement for capital adequacy with capital buffer, ratio	0.040	0.040
To qualify as well-capitalized under prompt corrective action provision, amount	$ 630,804	$ 619,701
To qualify as well-capitalized under prompt corrective action provision, ratio	0.050	0.050