Consolidated statements of comprehensive income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (5,599)	$ 23,966	$ 18,019	$ 62,242
Other comprehensive income, net of tax:
Net change in unrealized gain in available-for-sale securities, net of taxes of $521, $1,296, $5,225, and $6,430	1,788	3,762	15,091	18,265
Reclassification adjustment for (gain) loss on sale of securities included in net income, net of taxes of $(137), $20, $(137), and $20	(387)	55	(387)	56
Net change in unrealized gain (loss) in hedging activities, net of taxes of $40, $(90), $(403), and $(407)	112	(256)	(1,145)	(1,151)
Reclassification adjustment for gain on hedging activities, net of taxes of $(41), $(46), $(145), and $(121)	(115)	(130)	(410)	(343)
Total other comprehensive income, net of tax	1,398	3,431	13,149	16,827
Comprehensive (loss) income	(4,201)	27,397	31,168	79,069
Comprehensive (loss) income applicable to noncontrolling interests	0	0	0	0
Comprehensive (loss) income applicable to FB Financial Corporation	$ (4,201)	$ 27,397	$ 31,168	$ 79,069