Segment Reporting - Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 103,660	$ 88,182
Provision for credit losses	(491)	(4,247)
Mortgage banking income	15,493	29,278
Change in fair value of mortgage servicing rights, net of hedging	(3,407)	253
Other noninterest income	11,263	11,861
Depreciation and amortization	2,228	2,036
Amortization of intangibles	990	1,244
Other noninterest expense	77,222	85,992
Income before income taxes	46,078	44,549
Income tax expense	9,697	9,313
Net income attributable to FB Financial Corporation and noncontrolling interest	36,381	35,236
Net income applicable to noncontrolling interest	0	0
Net income applicable to FB Financial Corporation	36,381	35,236
Total assets	13,101,147	12,674,191	$ 12,847,756
Goodwill	242,561	242,561	$ 242,561
Provision for credit losses	4,997	(6,129)
Provision (reversal) for credit losses on unfunded commitments	(4,506)	1,882
Banking
Segment Reporting Information [Line Items]
Net interest income	103,660	88,184
Provision for credit losses	(491)	(4,247)
Mortgage banking income	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0
Other noninterest income	11,493	11,983
Depreciation and amortization	2,049	1,710
Amortization of intangibles	990	1,244
Other noninterest expense	65,311	56,630
Income before income taxes	46,312	44,830
Total assets	12,530,039	11,890,847
Goodwill	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	0	(2)
Provision for credit losses	0	0
Mortgage banking income	15,493	29,278
Change in fair value of mortgage servicing rights, net of hedging	(3,407)	253
Other noninterest income	(230)	(122)
Depreciation and amortization	179	326
Amortization of intangibles	0	0
Other noninterest expense	11,911	29,362
Income before income taxes	(234)	(281)
Total assets	571,108	783,344
Goodwill	$ 0	$ 0