Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Interest income	$ 725,538	$ 678,410	$ 481,422
Interest expense	309,035	271,193	69,187
Net interest income	416,503	407,217	412,235
Provisions for (reversals of) credit losses	12,004	2,539	18,982
Net interest income after provision for credit losses	404,499	404,678	393,253
Mortgage banking income	62,912	60,918	83,679
Change in fair value of mortgage servicing rights, net of hedging	(16,278)	(16,226)	(10,099)
Other noninterest (loss) income	(7,564)	25,851	41,087
Total noninterest income	39,070	70,543	114,667
Salaries, commissions and employee benefits	183,813	203,441	211,491
Depreciation and amortization	11,966	11,180	8,017
Amortization of intangibles	2,947	3,659	4,585
Other noninterest expense	98,173	106,649	124,253
Total noninterest expense	296,899	324,929	348,346
Income before income taxes	146,670	150,292	159,574
Income tax expense	30,619	30,052	35,003
Net income applicable to FB Financial Corporation and noncontrolling interest	116,051	120,240	124,571
Net income applicable to noncontrolling interest	16	16	16
Net income applicable to FB Financial Corporation	116,035	120,224	124,555
Total assets	13,157,482	12,604,403	12,847,756
Goodwill	242,561	242,561	242,561
Banking Segment
Segment Reporting Information [Line Items]
Interest income	726,033	678,591	470,430
Interest expense	315,250	277,342	71,405
Net interest income	410,783	401,249	399,025
Provisions for (reversals of) credit losses	12,264	2,599	18,982
Net interest income after provision for credit losses	398,519	398,650	380,043
Mortgage banking income	0	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0	0
Other noninterest (loss) income	(8,376)	25,831	41,312
Total noninterest income	(8,376)	25,831	41,312
Salaries, commissions and employee benefits	154,411	170,625	150,408
Depreciation and amortization	11,541	10,444	7,035
Amortization of intangibles	2,947	3,659	4,585
Other noninterest expense	78,172	85,407	63,248
Total noninterest expense	247,071	270,135	225,276
Income before income taxes	143,072	154,346	196,079
Total assets	12,554,435	12,050,245	12,232,849
Goodwill	242,561	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Interest income	(495)	(181)	10,992
Interest expense	(6,215)	(6,149)	(2,218)
Net interest income	5,720	5,968	13,210
Provisions for (reversals of) credit losses	(260)	(60)	0
Net interest income after provision for credit losses	5,980	6,028	13,210
Mortgage banking income	62,912	60,918	83,679
Change in fair value of mortgage servicing rights, net of hedging	(16,278)	(16,226)	(10,099)
Other noninterest (loss) income	812	20	(225)
Total noninterest income	47,446	44,712	73,355
Salaries, commissions and employee benefits	29,402	32,816	61,083
Depreciation and amortization	425	736	982
Amortization of intangibles	0	0	0
Other noninterest expense	20,001	21,242	61,005
Total noninterest expense	49,828	54,794	123,070
Income before income taxes	3,598	(4,054)	(36,505)
Total assets	603,047	554,158	614,907
Goodwill	$ 0	$ 0	$ 0