| 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 |
