Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	001-37875
Entity Registrant Name	FB FINANCIAL CORPORATION
Entity Incorporation, State or Country Code	TN
Entity Tax Identification Number	62-1216058
Entity Address, Address Line One	211 Commerce Street
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Nashville
Entity Address, State or Province	TN
Entity Address, Postal Zip Code	37201
City Area Code	615
Local Phone Number	564-1212
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Smaller Reporting Company	false
Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		32,103,348
Title of 12(b) Security	Common Stock, Par Value $1.00 Per Share
Trading Symbol	FBK
Security Exchange Name	NYSE
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001649749
Current Fiscal Year End Date	--12-31