Minimum Capital Requirements - Schedule of Actual and Required Capital Amounts and Ratios (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
FB Financial Corporation
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total Capital (to risk-weighted assets), Actual Amount	$ 338,893	$ 246,168
Total Capital (to risk-weighted assets), Actual Ratio	13.03%	11.15%
Total Capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 208,069	$ 176,623
Total Capital (to risk-weighted assets), For capital adequacy purposes, Ratio	8.00%	8.00%
Total Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Amount	$ 224,325
Total Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Ratio	8.63%
Tier 1 Capital (to risk-weighted assets), Actual Amount	$ 317,146	$ 211,633
Tier 1 Capital (to risk-weighted assets), Actual Ratio	12.19%	9.58%
Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 156,101	$ 132,547
Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Ratio	6.00%	6.00%
Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Amount	$ 172,362
Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Ratio	6.63%
Tier 1 Capital (to average assets), Actual Amount	$ 317,146	$ 211,633
Tier 1 Capital (to average assets), Actual Ratio	10.05%	7.64%
Tier 1 Capital (to average assets), For capital adequacy purposes, Amount	$ 126,227	$ 110,803
Tier 1 Capital (to average assets), For capital adequacy purposes, Ratio	4.00%	4.00%
Common Equity Tier 1 Capital (to risk-weighted assets), Actual Amount	$ 287,146	$ 181,633
Common Equity Tier 1 Capital (to risk-weighted assets), Actual Ratio	11.04%	8.23%
Common Equity Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 117,043	$ 99,313
Common Equity Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Ratio	4.50%	4.50%
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Amount	$ 133,299
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Ratio	5.13%
FirstBank
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total Capital (to risk-weighted assets), Actual Amount	$ 304,018	$ 242,240
Total Capital (to risk-weighted assets), Actual Ratio	11.72%	11.02%
Total Capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 207,521	$ 175,855
Total Capital (to risk-weighted assets), For capital adequacy purposes, Ratio	8.00%	8.00%
Total Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Amount	$ 223,733
Total Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Ratio	8.63%
Total Capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions, Amount	$ 259,401	$ 219,819
Total Capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions, Ratio	10.00%	10.00%
Tier 1 Capital (to risk-weighted assets), Actual Amount	$ 282,271	$ 211,780
Tier 1 Capital (to risk-weighted assets), Actual Ratio	10.88%	9.63%
Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 155,664	$ 131,950
Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Ratio	6.00%	6.00%
Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Amount	$ 171,879
Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Ratio	6.63%
Tier 1 Capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions Amount	$ 155,664	$ 131,950
Tier 1 Capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions Ratio	6.00%	6.00%
Tier 1 Capital (to average assets), Actual Amount	$ 282,271	$ 211,780
Tier 1 Capital (to average assets), Actual Ratio	8.95%	7.65%
Tier 1 Capital (to average assets), For capital adequacy purposes, Amount	$ 126,155	$ 110,735
Tier 1 Capital (to average assets), For capital adequacy purposes, Ratio	4.00%	4.00%
Tier 1 Capital (to average assets), To be well capitalized under prompt corrective action provisions, Amount	$ 157,693	$ 138,418
Tier 1 Capital (to average assets), To be well capitalized under prompt corrective action provisions, Ratio	5.00%	5.00%
Common Equity Tier 1 Capital (to risk-weighted assets), Actual Amount	$ 282,271	$ 211,780
Common Equity Tier 1 Capital (to risk-weighted assets), Actual Ratio	10.88%	9.63%
Common Equity Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Amount	$ 116,748	$ 98,963
Common Equity Tier 1 Capital (to risk-weighted assets), For capital adequacy purposes, Ratio	4.50%	4.50%
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Amount	$ 132,963
Common Equity Tier 1 Capital (to risk-weighted assets), Minimum Capital adequacy with capital buffer, Ratio	5.13%
Common Equity Tier 1 Capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions, Amount	$ 168,636	$ 142,946
Common Equity Tier 1 Capital (to risk-weighted assets), To be well capitalized under prompt corrective action provisions, Ratio	6.50%	6.50%