Minimum capital requirements (Details) $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
FB Financial Corporation
Total Capital (to risk-weighted assets)
Actual, Amount	$ 1,353,195	$ 1,358,897
Actual, Ratio	0.146	0.150
Minimum Capital adequacy with capital buffer, Amount	$ 972,054	$ 952,736
Minimum Capital adequacy with capital buffer, Ratio	0.105	0.105
Tier 1 Capital (to risk-weighted assets)
Actual, Amount	$ 1,138,657	$ 1,090,364
Actual, Ratio	0.123	0.120
Minimum Capital adequacy with capital buffer, Amount	$ 786,901	$ 771,262
Minimum Capital adequacy with capital buffer, Ratio	8.50%	8.50%
Tier 1 Capital (to average assets)
Actual, Amount	$ 1,138,657	$ 1,090,364
Actual, Ratio	0.101	0.100
Minimum Capital adequacy with capital buffer, Amount	$ 450,971	$ 435,064
Minimum Capital adequacy with capital buffer. Ratio	0.040	0.040
Common Equity Tier 1 Capital (to risk-weighted assets)
Actual, Amount	$ 1,108,657	$ 1,060,364
Actual Ratio	12.00%	11.70%
Minimum Capital adequacy with capital buffer, Amount	$ 648,036	$ 635,157
Minimum Capital adequacy with capital buffer, Ratio	0.070	0.070
FirstBank
Total Capital (to risk-weighted assets)
Actual, Amount	$ 1,316,420	$ 1,353,279
Actual, Ratio	0.142	0.149
Minimum Capital adequacy with capital buffer, Amount	$ 970,431	$ 951,327
Minimum Capital adequacy with capital buffer, Ratio	0.105	0.105
To be well capitalized under prompt corrective action provisions, Amount	$ 924,220	$ 906,026
To be well capitalized under prompt corrective action provisions, Ratio	0.100	0.100
Tier 1 Capital (to risk-weighted assets)
Actual, Amount	$ 1,121,997	$ 1,142,548
Actual, Ratio	0.121	0.126
Minimum Capital adequacy with capital buffer, Amount	$ 785,587	$ 770,122
Minimum Capital adequacy with capital buffer, Ratio	8.50%	8.50%
To be well capitalized under prompt corrective action provisions Amount	$ 739,376	$ 724,820
To be well capitalized under prompt corrective action provisions Ratio	0.080	0.080
Tier 1 Capital (to average assets)
Actual, Amount	$ 1,121,997	$ 1,142,548
Actual, Ratio	0.100	0.105
Minimum Capital adequacy with capital buffer, Amount	$ 450,889	$ 435,279
Minimum Capital adequacy with capital buffer. Ratio	0.040	0.040
To be well capitalized under prompt corrective action provisions, Amount	$ 563,611	$ 544,098
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	$ 1,121,997	$ 1,142,548
Actual Ratio	12.10%	12.60%
Minimum Capital adequacy with capital buffer, Amount	$ 646,954	$ 634,218
Minimum Capital adequacy with capital buffer, Ratio	0.070	0.070
To be well capitalized under prompt corrective action provisions, Amount	$ 600,743	$ 588,917
To be well capitalized under prompt corrective action provisions, Ratio	6.50%	6.50%