Segment Reporting - Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 101,543	$ 102,171	$ 205,203	$ 190,353
Provisions for credit losses	1,078	12,318	587	8,071
Mortgage banking income	16,454	23,711	31,947	52,989
Change in fair value of mortgage servicing rights, net of hedging	(4,222)	(1,152)	(7,629)	(899)
Other noninterest income	11,581	10,655	22,844	22,516
Depreciation and amortization	2,452	2,012	4,680	4,048
Amortization of intangibles	940	1,194	1,930	2,438
Other noninterest expense	77,900	93,791	155,122	179,783
Income before income taxes	45,142	26,070	91,220	70,619
Income tax expense	9,835	6,717	19,532	16,030
Net income attributable to FB Financial Corporation and noncontrolling interest	35,307	19,353	71,688	54,589
Net income applicable to noncontrolling interest	8	8	8	8
Net income applicable to FB Financial Corporation	35,299	19,345	71,680	54,581
Total assets	12,887,395	12,193,862	12,887,395	12,193,862	$ 12,847,756
Goodwill	242,561	242,561	242,561	242,561	$ 242,561
Mortgage restructuring expense	0	12,458	0	12,458
Banking
Segment Reporting Information [Line Items]
Net interest income	101,543	102,171	205,203	190,355
Provisions for credit losses	1,078	12,318	587	8,071
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	11,480	10,699	22,973	22,682
Depreciation and amortization	2,220	1,731	4,269	3,441
Amortization of intangibles	940	1,194	1,930	2,438
Other noninterest expense	64,493	56,395	129,804	113,025
Income before income taxes	46,448	41,232	92,760	86,062
Total assets	12,302,812	11,469,762	12,302,812	11,469,762
Goodwill	242,561	242,561	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	0	0	0	(2)
Provisions for credit losses	0	0	0	0
Mortgage banking income	16,454	23,711	31,947	52,989
Change in fair value of mortgage servicing rights, net of hedging	(4,222)	(1,152)	(7,629)	(899)
Other noninterest income	101	(44)	(129)	(166)
Depreciation and amortization	232	281	411	607
Amortization of intangibles	0	0	0	0
Other noninterest expense	13,407	37,396	25,318	66,758
Income before income taxes	(1,306)	(15,162)	(1,540)	(15,443)
Total assets	584,583	724,100	584,583	724,100
Goodwill	$ 0	$ 0	$ 0	$ 0