Mergers and Acquisitions - Schedule of Unaudited Pro Forma Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Business Combination, Pro Forma Information [Line Items]
Merger and integration costs	$ 16,057	$ 0	$ 19,192	$ 0
Provision expense for credit losses on acquired loans and unfunded commitments	34,417	1,914	42,046	4,920
Net interest income	143,783	134,597	419,954	389,691
Total revenues	170,418	119,857	426,430	410,887
Net income applicable to FB Financial Corporation	41,977	$ 19,716	90,846	$ 88,578
Southern States Bancshares, Inc.
Business Combination, Pro Forma Information [Line Items]
Merger and integration costs	16,057		$ 19,192
Provision expense for credit losses on acquired loans and unfunded commitments	$ 28,366