Segment Reporting - Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 88,182	$ 82,576
Provision for credit losses	(4,247)	(13,854)
Mortgage banking income	29,278	60,595
Change in fair value of mortgage servicing rights, net of hedging	253	(5,263)
Other noninterest income	11,861	11,398
Depreciation and amortization	2,036	2,056
Amortization of intangibles	1,244	1,440
Other noninterest expense	85,992	91,202
Income (loss) before income taxes	44,549	68,462
Income tax expense	9,313	15,588
Net income applicable to FB Financial Corporation and noncontrolling interest	35,236	52,874
Net income applicable to noncontrolling interest	0	0
Net income applicable to FB Financial Corporation	35,236	52,874
Assets	12,674,191	11,935,826	$ 12,597,686
Goodwill	242,561	242,561	$ 242,561
Provision (reversal) for credit losses on unfunded commitments	1,882	(2,222)
Banking
Segment Reporting Information [Line Items]
Net interest income	88,184	82,597
Provision for credit losses	(4,247)	(13,854)
Mortgage banking income	0	0
Change in fair value of mortgage servicing rights, net of hedging	0	0
Other noninterest income	11,983	11,398
Depreciation and amortization	1,710	1,728
Amortization of intangibles	1,244	1,440
Other noninterest expense	56,630	52,567
Income (loss) before income taxes	44,830	52,114
Assets	11,890,847	10,787,955
Goodwill	242,561	242,561
Mortgage
Segment Reporting Information [Line Items]
Net interest income	(2)	(21)
Provision for credit losses	0	0
Mortgage banking income	29,278	60,595
Change in fair value of mortgage servicing rights, net of hedging	253	(5,263)
Other noninterest income	(122)	0
Depreciation and amortization	326	328
Amortization of intangibles	0	0
Other noninterest expense	29,362	38,635
Income (loss) before income taxes	(281)	16,348
Assets	783,344	1,147,871
Goodwill	$ 0	$ 0