Segment Reporting - Segment Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net interest income	$ 412,235	$ 347,370	$ 265,658
Provision for credit losses	18,982	(40,993)	107,967
Mortgage banking income	83,679	179,682	289,702
Change in fair value of mortgage servicing rights, net of hedging	(10,099)	(12,117)	(34,374)
Other noninterest income	41,087	60,690	46,527
Depreciation and amortization	8,017	8,416	7,536
Amortization of intangibles	4,585	5,473	5,323
Other noninterest expense	335,744	359,678	364,226
Income before income taxes	159,574	243,051	82,461
Income tax expense	35,003	52,750	18,832
Net income applicable to FB Financial Corporation and noncontrolling interest	124,571	190,301	63,629
Net income applicable to noncontrolling interest	16	16	8
Net income applicable to FB Financial Corporation	124,555	190,285	63,621
Total assets	12,847,756	12,597,686	11,207,330
Goodwill	242,561	242,561	242,561
Provision (reversal) for credit losses on unfunded commitments	8,589	(1,998)	13,361
Mortgage restructuring expense	12,458	0	0
Merger costs	0	0	34,879
Banking
Segment Reporting Information [Line Items]
Net interest income	412,237	347,342	265,581
Provision for credit losses	18,982	(40,993)	107,967
Mortgage banking income	0	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0	0
Other noninterest income	41,320	61,073	46,527
Depreciation and amortization	7,035	7,054	6,425
Amortization of intangibles	4,585	5,473	5,323
Other noninterest expense	240,096	220,283	212,890
Income before income taxes	182,859	216,598	(20,497)
Total assets	12,228,451	11,540,560	10,254,324
Goodwill	242,561	242,561	242,561
Banking | Segment Realignment, Reclassification Adjustment
Segment Reporting Information [Line Items]
Income before income taxes			26,416
Mortgage
Segment Reporting Information [Line Items]
Net interest income	(2)	28	77
Provision for credit losses	0	0	0
Mortgage banking income	83,679	179,682	289,702
Change in fair value of mortgage servicing rights, net of hedging	(10,099)	(12,117)	(34,374)
Other noninterest income	(233)	(383)	0
Depreciation and amortization	982	1,362	1,111
Amortization of intangibles	0	0	0
Other noninterest expense	95,648	139,395	151,336
Income before income taxes	(23,285)	26,453	102,958
Total assets	619,305	1,057,126	953,006
Goodwill	0	$ 0	0
Pre tax restructuring charges	$ 12,458
Mortgage | Segment Realignment, Reclassification Adjustment
Segment Reporting Information [Line Items]
Income before income taxes			26,416
Mortgage | Atlantic Capital
Segment Reporting Information [Line Items]
Other noninterest expense			1,055
Merger costs			$ 33,824