Document And Entity Information - USD ($)	Dec. 31, 2020	Mar. 08, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity, Registrant Name	NATIONAL BANKSHARES, INC.
Current Fiscal Year End Date	--12-31
Document, Fiscal Period Focus	FY
Document, Fiscal Year Focus	2020
Document, Type	10-K/A
Document, Annual Report	true
Document, Period End Date	Dec. 31, 2020
Document, Transition Report	false
Entity, File Number	0-15204
Entity, Incorporation, State or Country Code	VA
Entity, Tax Identification Number	54-1375874
Entity, Address, Address Line One	101 Hubbard Street
Entity, Address, City or Town	Blacksburg
Entity, Address, State or Province	VA
Entity, Address, Postal Zip Code	24062-9002
City Area Code	540
Local Phone Number	951-6300
Title of 12(b) Security	Common Stock
Trading Symbol	NKSH
Security Exchange Name	NASDAQ
Entity, Well-known Seasoned Issuer	No
Entity, Voluntary Filers	No
Entity, Current Reporting Status	Yes
Entity, Interactive Data, Current	Yes
Entity, Filer Category	Non-accelerated Filer
Entity, Small Business	true
Entity, Emerging Growth Company	false
Entity, Shell Company	false
Entity, Public Float			$ 185,601,816
Entity, Common Stock Shares, Outstanding		6,388,120
Amendment Description	National Bankshares, Inc. (the “Company”) is filing this Amendment No. 1 on Form 10-K/A (the “Form 10-K/A”) to amend its Annual Report on Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission (the “SEC”) on March 18, 2021 (the “Original Form 10-K” and, together with the Form 10-K/A, the “Form 10-K”). This Form 10-K/A is being filed solely for the following reasons:
Amendment Flag	true
Entity, Central Index Key	0000796534