Minimum Capital Requirements (Details) $ in Thousands	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
FB Financial Corporation
Total Capital (to risk-weighted assets)
Actual, amount	$ 1,923,161	$ 1,721,941
Actual, ratio	0.136	0.152
Minimum requirement for capital adequacy with capital buffer, amount	$ 1,488,143	$ 1,187,163
Minimum requirement for capital adequacy with capital buffer, ratio	0.105	0.105
Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,662,376	$ 1,480,722
Actual, ratio	0.117	0.131
Minimum requirement for capital adequacy with capital buffer, amount	$ 1,204,687	$ 961,037
Minimum requirement for capital adequacy with capital buffer, ratio	0.085	0.085
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,662,376	$ 1,450,722
Actual, ratio	0.117	0.128
Minimum requirement for capital adequacy with capital buffer, amount	$ 992,095	$ 791,442
Minimum requirement for capital adequacy with capital buffer, ratio	0.070	0.070
Tier 1 Capital (to average assets)
Actual, amount	$ 1,662,376	$ 1,480,722
Actual, ratio	0.106	0.113
Minimum requirement for capital adequacy with capital buffer, amount	$ 628,731	$ 522,557
Minimum requirement for capital adequacy with capital buffer, ratio	0.040	0.040
FirstBank
Total Capital (to risk-weighted assets)
Actual, amount	$ 1,863,890	$ 1,650,305
Actual, ratio	0.133	0.147
Minimum requirement for capital adequacy with capital buffer, amount	$ 1,475,854	$ 1,175,095
Minimum requirement for capital adequacy with capital buffer, ratio	0.105	0.105
To qualify as well-capitalized under prompt corrective action provision, amount	$ 1,405,575	$ 1,119,138
To qualify as well-capitalized under prompt corrective action provision, ratio	0.100	0.100
Tier 1 Capital (to risk-weighted assets)
Actual, amount	$ 1,687,888	$ 1,410,505
Actual, ratio	0.120	0.126
Minimum requirement for capital adequacy with capital buffer, amount	$ 1,194,739	$ 951,267
Minimum requirement for capital adequacy with capital buffer, ratio	0.085	0.085
To qualify as well-capitalized under prompt corrective action provision, amount	$ 1,124,460	$ 895,310
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	$ 1,687,888	$ 1,410,505
Actual, ratio	0.120	0.126
Minimum requirement for capital adequacy with capital buffer, amount	$ 983,903	$ 783,397
Minimum requirement for capital adequacy with capital buffer, ratio	0.070	0.070
To qualify as well-capitalized under prompt corrective action provision, amount	$ 913,624	$ 727,440
To qualify as well-capitalized under prompt corrective action provision, ratio	0.065	0.065
Tier 1 Capital (to average assets)
Actual, amount	$ 1,687,888	$ 1,410,505
Actual, ratio	0.108	0.108
Minimum requirement for capital adequacy with capital buffer, amount	$ 626,042	$ 521,538
Minimum requirement for capital adequacy with capital buffer, ratio	0.040	0.040
To qualify as well-capitalized under prompt corrective action provision, amount	$ 782,552	$ 651,923
To qualify as well-capitalized under prompt corrective action provision, ratio	0.050	0.050