Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Net interest income	$ 106,017	$ 100,926	$ 308,122	$ 306,129
Provisions for (reversals of) credit losses	1,914	2,821	4,920	2,234
Mortgage banking income	16,043	15,722	47,915	47,669
Change in fair value of mortgage servicing rights, net of hedging	(4,490)	(3,724)	(11,867)	(11,353)
Other noninterest (loss) income	(28,050)	(3,956)	(18,975)	18,888
Depreciation and amortization	3,255	2,681	8,957	7,361
Amortization of intangibles	719	889	2,260	2,819
Other noninterest mortgage banking expense	0	0
Other noninterest expense	72,238	79,427	212,508	234,549
Income before income taxes	11,394	23,150	96,550	114,370
Income tax expense	1,174	3,975	18,393	23,507
Net income attributable to FB Financial Corporation and noncontrolling interest	10,220	19,175	78,157	90,863
Net income applicable to noncontrolling interest	0	0	8	8
Net income applicable to FB Financial Corporation	10,220	19,175	78,149	90,855
Total assets	12,920,222	12,489,631	12,920,222	12,489,631	$ 12,604,403
Goodwill	242,561	242,561	242,561	242,561	$ 242,561
Banking
Segment Reporting Information [Line Items]
Net interest income	104,335	99,359	303,990	301,438
Provisions for (reversals of) credit losses	1,861	3,253	5,131	2,316
Mortgage banking income	0	0	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0	0	0
Other noninterest (loss) income	(28,370)	(4,031)	(19,687)	18,942
Depreciation and amortization	3,141	2,514	8,594	6,783
Amortization of intangibles	719	889	2,260	2,819
Other noninterest mortgage banking expense	0	0
Other noninterest expense	59,425	65,309	175,104	192,070
Income before income taxes	10,819	23,363	93,214	116,392
Total assets	12,337,135	11,904,608	12,337,135	11,904,608
Goodwill	242,561	242,561	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	1,682	1,567	4,132	4,691
Provisions for (reversals of) credit losses	53	(432)	(211)	(82)
Mortgage banking income	16,043	15,722	47,915	47,669
Change in fair value of mortgage servicing rights, net of hedging	(4,490)	(3,724)	(11,867)	(11,353)
Other noninterest (loss) income	320	75	712	(54)
Depreciation and amortization	114	167	363	578
Amortization of intangibles	0	0	0	0
Other noninterest mortgage banking expense	0	0
Other noninterest expense	12,813	14,118	37,404	42,479
Income before income taxes	575	(213)	3,336	(2,022)
Total assets	583,087	585,023	583,087	585,023
Goodwill	$ 0	$ 0	$ 0	$ 0