Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 407,217	$ 412,235	$ 347,370
Provisions for credit losses	2,539	18,982	(40,993)
Mortgage banking income	60,918	83,679	179,682
Change in fair value of mortgage servicing rights, net of hedging	(16,226)	(10,099)	(12,117)
Other noninterest income	25,851	41,087	60,690
Depreciation and amortization	11,180	8,017	8,416
Amortization of intangibles	3,659	4,585	5,473
Other noninterest expense	310,090	335,744	359,678
Income before income taxes	150,292	159,574	243,051
Income tax expense	30,052	35,003	52,750
Net income attributable to FB Financial Corporation and noncontrolling interest	120,240	124,571	190,301
Net income applicable to noncontrolling interest	16	16	16
Net income applicable to FB Financial Corporation	120,224	124,555	190,285
Total assets	12,604,403	12,847,756	12,597,686
Goodwill	242,561	242,561	242,561
Mortgage restructuring expense	0	12,458	0
Banking
Segment Reporting Information [Line Items]
Net interest income	407,217	412,237	347,342
Provisions for credit losses	2,539	18,982	(40,993)
Mortgage banking income	0	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0	0
Other noninterest income	25,831	41,320	61,073
Depreciation and amortization	10,444	7,035	7,054
Amortization of intangibles	3,659	4,585	5,473
Other noninterest expense	262,433	240,096	220,283
Income before income taxes	153,973	182,859	216,598
Total assets	12,046,190	12,228,451	11,540,560
Goodwill	242,561	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	0	(2)	28
Provisions for credit losses	0	0	0
Mortgage banking income	60,918	83,679	179,682
Change in fair value of mortgage servicing rights, net of hedging	(16,226)	(10,099)	(12,117)
Other noninterest income	20	(233)	(383)
Depreciation and amortization	736	982	1,362
Amortization of intangibles	0	0	0
Other noninterest expense	47,657	95,648	139,395
Income before income taxes	(3,681)	(23,285)	26,453
Total assets	558,213	619,305	1,057,126
Goodwill	$ 0	$ 0	$ 0