Segment Reporting - Schedule of Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Net interest income	$ 102,615	$ 101,543	$ 202,105	$ 205,203
Provisions for (reversal of) credit losses	2,224	(1,078)	3,006	(587)
Mortgage banking income	16,246	16,454	31,872	31,947
Change in fair value of mortgage servicing rights, net of hedging	(4,336)	(4,222)	(7,377)	(7,629)
Other noninterest income	13,698	11,581	9,075	22,844
Depreciation and amortization	2,861	2,452	5,702	4,680
Amortization of intangibles	752	940	1,541	1,930
Other noninterest mortgage banking expense	0	0
Other noninterest expense	71,480	77,900	140,270	155,122
Income before income taxes	50,906	45,142	85,156	91,220
Income tax expense	10,919	9,835	17,219	19,532
Net income attributable to FB Financial Corporation and noncontrolling interest	39,987	35,307	67,937	71,688
Net income applicable to noncontrolling interest	8	8	8	8
Net income applicable to FB Financial Corporation	39,979	35,299	67,929	71,680
Total assets	12,535,169	12,887,395	12,535,169	12,887,395	$ 12,604,403
Goodwill	242,561	242,561	242,561	242,561	$ 242,561
Banking
Segment Reporting Information [Line Items]
Net interest income	101,468	99,909	200,205	202,179
Provisions for (reversal of) credit losses	2,432	(1,149)	3,270	(937)
Mortgage banking income	0	0	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0	0	0
Other noninterest income	13,477	11,480	8,683	22,973
Depreciation and amortization	2,745	2,220	5,453	4,269
Amortization of intangibles	752	940	1,541	1,930
Other noninterest mortgage banking expense	0	0
Other noninterest expense	58,832	63,048	115,679	126,761
Income before income taxes	50,184	46,330	82,945	93,129
Total assets	11,947,550	12,307,231	11,947,550	12,307,231
Goodwill	242,561	242,561	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	1,147	1,634	1,900	3,024
Provisions for (reversal of) credit losses	(208)	71	(264)	350
Mortgage banking income	16,246	16,454	31,872	31,947
Change in fair value of mortgage servicing rights, net of hedging	(4,336)	(4,222)	(7,377)	(7,629)
Other noninterest income	221	101	392	(129)
Depreciation and amortization	116	232	249	411
Amortization of intangibles	0	0	0	0
Other noninterest mortgage banking expense	0	0
Other noninterest expense	12,648	14,852	24,591	28,361
Income before income taxes	722	(1,188)	2,211	(1,909)
Total assets	587,619	580,164	587,619	580,164
Goodwill	$ 0	$ 0	$ 0	$ 0