Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Segment Reporting Information [Line Items]
Interest income	$ 179,706	$ 176,128
Interest expense	72,065	76,638
Net interest income	107,641	99,490
Provisions for (reversals of) credit losses	2,292	782
Net interest income after provision for credit losses	105,349	98,708
Mortgage banking income	15,495	15,626
Change in fair value of mortgage servicing rights, net of hedging	(3,069)	(3,041)
Other noninterest income (loss)	10,606	(4,623)
Total noninterest (loss) income	23,032	7,962
Salaries, commissions and employee benefits	48,351	44,618
Depreciation and amortization	2,767	2,841
Amortization of intangibles	656	789
Other noninterest expense	27,775	24,172
Total noninterest expense	79,549	72,420
Income before income taxes	48,832	34,250
Income tax expense	9,471	6,300
Net income applicable to FB Financial Corporation and noncontrolling interest	39,361	27,950
Net income applicable to noncontrolling interest	0	0
Net income applicable to FB Financial Corporation	39,361	27,950
Total assets	13,136,449	12,548,320	$ 13,157,482
Goodwill	242,561	242,561	$ 242,561
Banking
Segment Reporting Information [Line Items]
Interest income	178,915	176,420
Interest expense	73,156	77,958
Net interest income	105,759	98,462
Provisions for (reversals of) credit losses	2,189	838
Net interest income after provision for credit losses	103,570	97,624
Mortgage banking income	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0
Other noninterest income (loss)	10,660	(4,794)
Total noninterest (loss) income	10,660	(4,794)
Salaries, commissions and employee benefits	41,469	37,790
Depreciation and amortization	2,743	2,708
Amortization of intangibles	656	789
Other noninterest expense	22,041	18,908
Total noninterest expense	66,909	60,195
Income before income taxes	47,321	32,635
Total assets	12,490,097	11,979,904
Goodwill	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Interest income	791	(292)
Interest expense	(1,091)	(1,320)
Net interest income	1,882	1,028
Provisions for (reversals of) credit losses	103	(56)
Net interest income after provision for credit losses	1,779	1,084
Mortgage banking income	15,495	15,626
Change in fair value of mortgage servicing rights, net of hedging	(3,069)	(3,041)
Other noninterest income (loss)	(54)	171
Total noninterest (loss) income	12,372	12,756
Salaries, commissions and employee benefits	6,882	6,828
Depreciation and amortization	24	133
Amortization of intangibles	0	0
Other noninterest expense	5,734	5,264
Total noninterest expense	12,640	12,225
Income before income taxes	1,511	1,615
Total assets	646,352	568,416
Goodwill	$ 0	$ 0