Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Document Information [Line Items]
Entity Central Index Key	0000741516
Entity Registrant Name	AMERICAN NATIONAL BANKSHARES INC.
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	0-12820
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	54-1284688
Entity Address, Address Line One	628 Main Street
Entity Address, City or Town	Danville
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	24541
City Area Code	434
Local Phone Number	792-5111
Title of 12(b) Security	Common Stock
Trading Symbol	AMNB
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		10,778,728