Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 100,926	$ 111,384	$ 306,129	$ 301,737
Provisions for credit losses	(2,821)	11,367	(2,234)	19,438
Mortgage banking income	15,722	16,729	47,669	69,718
Change in fair value of mortgage servicing rights, net of hedging	(3,724)	(4,345)	(11,353)	(5,244)
Other noninterest income	(3,956)	10,208	18,888	32,724
Depreciation and amortization	2,681	2,057	7,361	6,105
Amortization of intangibles	889	1,108	2,819	3,546
Other noninterest expense	79,427	78,682	234,549	258,465
Income before income taxes	23,150	40,762	114,370	111,381
Income tax expense	3,975	8,931	23,507	24,961
Net income attributable to FB Financial Corporation and noncontrolling interest	19,175	31,831	90,863	86,420
Net income applicable to noncontrolling interest	0	0	8	8
Net income applicable to FB Financial Corporation	19,175	31,831	90,855	86,412
Total assets	12,489,631	12,258,082	12,489,631	12,258,082	$ 12,847,756
Goodwill	242,561	242,561	242,561	242,561	$ 242,561
Mortgage restructuring expense	0	0	0	12,458
Banking
Segment Reporting Information [Line Items]
Net interest income	100,926	111,384	306,129	301,739
Provisions for credit losses	(2,821)	11,367	(2,234)	19,438
Mortgage banking income	0	0	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0	0	0
Other noninterest income	(4,031)	10,293	18,942	32,975
Depreciation and amortization	2,514	1,867	6,783	5,308
Amortization of intangibles	889	1,108	2,819	3,546
Other noninterest expense	67,571	62,911	197,375	175,936
Income before income taxes	23,100	44,424	115,860	130,486
Total assets	11,900,598	11,648,610	11,900,598	11,648,610
Goodwill	242,561	242,561	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	0	0	0	(2)
Provisions for credit losses	0	0	0	0
Mortgage banking income	15,722	16,729	47,669	69,718
Change in fair value of mortgage servicing rights, net of hedging	(3,724)	(4,345)	(11,353)	(5,244)
Other noninterest income	75	(85)	(54)	(251)
Depreciation and amortization	167	190	578	797
Amortization of intangibles	0	0	0	0
Other noninterest expense	11,856	15,771	37,174	82,529
Income before income taxes	50	(3,662)	(1,490)	(19,105)
Total assets	589,033	609,472	589,033	609,472
Goodwill	$ 0	$ 0	$ 0	$ 0