Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	The consolidated financial statements include the accounts of American National Bankshares Inc. (NASDAQ: AMNB) (the "Company") and its wholly-owned subsidiary, American National Bank and Trust Company (the "Bank"). The Company is a multi-state bank holding company headquartered in Danville, Virginia. The Bank is a community bank organization serving Virginia and North Carolina with 26 banking offices. In addition to traditional retail, commercial and mortgage offerings, the Bank also provides trust and investment services through its Trust and Investment Services Division. The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America ("GAAP") requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for loan losses, goodwill and intangible assets, other-than-temporary impairment of securities, accounting for merger and acquisition activity, accounting for acquired loans with specific credit-related deterioration, and the valuation of deferred tax assets and liabilities. COVID-19 spread rapidly across the world in the first quarter of 2020 and was declared a pandemic by the World Health Organization. On March 13, 2020, the United States President declared a national emergency in the face of a growing public health and economic crisis due to the COVID-19 global pandemic. The government and private sector responses to contain its spread began to significantly affect the Company's operations beginning in March 2020 and will likely continue to adversely affect its operations through 2021, although such effects may vary significantly. The duration and extent of the effects over longer terms cannot be reasonably estimated at this time. The risks and uncertainties resulting from the pandemic will most likely affect future earnings, cash flows and overall financial condition of the Company. These uncertainties include the nature and duration of the financial effects felt by its customers impacting their ability to perform in accordance with their underlying loan agreements, the Company's ability to generate demand for non-loan related products and services, as well as potential declines in real estate values resulting from the market disruption which may impair the recorded values of collateral-dependent loans and other real estate owned. Further, these factors, in addition to those pervasive to the industry and overall U.S. economy, may necessitate an overall valuation of the Company's franchise in such a way an impairment charge to the carrying value of goodwill would be required. Accordingly, significant estimates used in the preparation of the Company's financial statements including those associated with the evaluation of the allowance for loan losses as well as other valuation-based estimates may be subject to significant adjustments in future periods. We have seen significant improvement in the severity of the pandemic, however, as it continues to affect economies around the world and in the United States, it could impact estimates in future periods. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments (consisting of normal recurring accruals) necessary to present fairly the results of the interim periods. The results of operations for the interim periods are not necessarily indicative of the results that may occur for any other period. These statements should be read in conjunction with the Notes to Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2020. Certain prior period balances have been reclassified to conform to the current period presentation.
New Accounting Pronouncements, Policy [Policy Text Block]	*Recently Adopted Accounting Developments* In December 2020, the Consolidated Appropriations Act of 2021 ("CAA") was passed. Under Section 541 of the CAA, Congress extended or modified many of the relief programs first created by the Coronavirus Aid, Relief, and Economic Security ("CARES") Act, including the Small Business Administration ("SBA") Paycheck Protection Program ("PPP") and treatment of certain loan modifications related to the COVID-19 pandemic. The Company utilized a Disaster Assistance Program for borrowers in accordance with Section 4013 of the CARES Act throughout the pandemic. The Company assisted borrowers with modifications to outstanding loan balances of $347.0 million in the aggregate since the beginning of the pandemic in March 2020. At September 30, 2021, all modifications had expired compared to outstanding loan balances of $2.3 million at June 30, 2021. The Company processed a total of $364.2 million in PPP loans with $66.9 million forgiven in the third quarter of 2021 compared to $80.0 million in the second quarter of 2021. The loans are 100% guaranteed by the SBA and therefore do not have a related allowance. The SBA paid the Bank a processing fee based on the size of the loan which is amortized to income over the life of the loan or until the loan is forgiven. Total outstanding net PPP loans were $37.2 million and $211.3 million at September 30, 2021 and December 31, 2020, respectively. Recent Accounting Pronouncements and Other Authoritative Accounting Guidance In June 2016, the FASB issued ASU 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." The amendments in this ASU, among other things, require the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to better inform their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the full amount of expected credit losses. In addition, the ASU amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The FASB has issued multiple updates to ASU 2016-13 as codified in Topic 326, including ASU's 2019-04, 2019-05, 2019-10, 2019-11, 2020-02, and 2020-03. These ASUs have provided for various minor technical corrections and improvements to the codification as well as other transition matters. Smaller reporting companies who file with the U.S. Securities and Exchange Commission ("SEC") and all other entities who do not file with the SEC are required to apply the guidance for fiscal years, and interim periods within those years, beginning after December 15, 2022. At the one-time evaluation date, the Company qualified as a smaller reporting company and elected to defer the adoption of the standard. The Company is refining the data in the model that will be used upon future adoption of the standard and expects to run concurrent models in the fourth quarter of 2021 and each quarter of 2022 until adoption. The implementation of this ASU will likely result in an adjustment to the Company's reserves when implemented. Effective November 25, 2019, the SEC adopted Staff Accounting Bulletin ("SAB") 119. SAB 119 updated portions of SEC interpretative guidance to align with ASC 326, Financial Instruments - Credit Losses. It covers topics including (1) measuring current expected credit losses; (2) development, governance, and documentation of a systematic methodology; (3) documenting the results of a systematic methodology; and (4) validating a systematic methodology. In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." The amendments in this ASU provide temporary optional guidance to ease the potential burden in accounting for reference rate reform. The ASU provides optional expedients and exceptions for applying generally accepted accounting principles to contract modifications and hedging relationships, subject to meeting certain criteria, that reference the London Interbank Offered Rate ("LIBOR") or another reference rate expected to be discontinued. It is intended to help stakeholders during the global market-wide reference rate transition period. The guidance is effective for all entities as of March 12, 2020 through December 31, 2022. Subsequently, in January 2021, the FASB issued ASU 2021-01, "Reference Rate Reform (Topic 848): Scope." This ASU clarifies that certain optional expedients and exceptions in Topic 848 for contract modifications and hedge accounting apply to derivatives that are affected by the discounting transition. The ASU also amends the expedients and exceptions in Topic 848 to capture the incremental consequences of the scope clarification and to tailor the existing guidance to derivative instruments affected by the discounting transition. An entity may elect to apply ASU 2021-01 on contract modifications that change the interest rate used for margining, discounting, or contract price alignment retrospectively as of any date from the beginning of the interim period that includes March 12, 2020, or prospectively to new modifications from any date within the interim period that includes or is subsequent to January 7, 2021, up to the date that financial statements are available to be issued. An entity may elect to apply ASU 2021-01 to eligible hedging relationships existing as of the beginning of the interim period that includes March 12, 2020, and to new eligible hedging relationships entered into after the beginning of the interim period that includes March 12, 2020. The Company does not expect the adoption of ASU 2020-04 to have a material impact on its consolidated financial statements.

In December 2020, the Consolidated Appropriations Act of 2021 ("CAA") was passed. Under Section 541 of the CAA, Congress extended or modified many of the relief programs first created by the Coronavirus Aid, Relief, and Economic Security ("CARES") Act, including the Small Business Administration ("SBA") Paycheck Protection Program ("PPP") and treatment of certain loan modifications related to the COVID-19 pandemic.

The Company utilized a Disaster Assistance Program for borrowers in accordance with Section 4013 of the CARES Act throughout the pandemic. The Company assisted borrowers with modifications to outstanding loan balances of $347.0 million in the aggregate since the beginning of the pandemic in March 2020. At September 30, 2021, all modifications had expired compared to outstanding loan balances of $2.3 million at June 30, 2021.

The Company processed a total of $364.2 million in PPP loans with $66.9 million forgiven in the third quarter of 2021 compared to $80.0 million in the second quarter of 2021. The loans are 100% guaranteed by the SBA and therefore do not have a related allowance. The SBA paid the Bank a processing fee based on the size of the loan which is amortized to income over the life of the loan or until the loan is forgiven. Total outstanding net PPP loans were $37.2 million and $211.3 million at September 30, 2021 and December 31, 2020, respectively.

Recent Accounting Pronouncements and Other Authoritative Accounting Guidance

In June 2016, the FASB issued ASU 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." The amendments in this ASU, among other things, require the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. Financial institutions and other organizations will now use forward-looking information to better inform their credit loss estimates. Many of the loss estimation techniques applied today will still be permitted, although the inputs to those techniques will change to reflect the full amount of expected credit losses. In addition, the ASU amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The FASB has issued multiple updates to ASU 2016-13 as codified in Topic 326, including ASU's 2019-04, 2019-05, 2019-10, 2019-11, 2020-02, and 2020-03. These ASUs have provided for various minor technical corrections and improvements to the codification as well as other transition matters. Smaller reporting companies who file with the U.S. Securities and Exchange Commission ("SEC") and all other entities who do not file with the SEC are required to apply the guidance for fiscal years, and interim periods within those years, beginning after December 15, 2022. At the one-time evaluation date, the Company qualified as a smaller reporting company and elected to defer the adoption of the standard. The Company is refining the data in the model that will be used upon future adoption of the standard and expects to run concurrent models in the fourth quarter of 2021 and each quarter of 2022 until adoption. The implementation of this ASU will likely result in an adjustment to the Company's reserves when implemented.

Effective November 25, 2019, the SEC adopted Staff Accounting Bulletin ("SAB") 119. SAB 119 updated portions of SEC interpretative guidance to align with ASC 326, Financial Instruments - Credit Losses. It covers topics including (1) measuring current expected credit losses; (2) development, governance, and documentation of a systematic methodology; (3) documenting the results of a systematic methodology; and (4) validating a systematic methodology.

In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." The amendments in this ASU provide temporary optional guidance to ease the potential burden in accounting for reference rate reform. The ASU provides optional expedients and exceptions for applying generally accepted accounting principles to contract modifications and hedging relationships, subject to meeting certain criteria, that reference the London Interbank Offered Rate ("LIBOR") or another reference rate expected to be discontinued. It is intended to help stakeholders during the global market-wide reference rate transition period. The guidance is effective for all entities as of March 12, 2020 through December 31, 2022. Subsequently, in January 2021, the FASB issued ASU 2021-01, "Reference Rate Reform (Topic 848): Scope." This ASU clarifies that certain optional expedients and exceptions in Topic 848 for contract modifications and hedge accounting apply to derivatives that are affected by the discounting transition. The ASU also amends the expedients and exceptions in Topic 848 to capture the incremental consequences of the scope clarification and to tailor the existing guidance to derivative instruments affected by the discounting transition. An entity may elect to apply ASU 2021-01 on contract modifications that change the interest rate used for margining, discounting, or contract price alignment retrospectively as of any date from the beginning of the interim period that includes March 12, 2020, or prospectively to new modifications from any date within the interim period that includes or is subsequent to January 7, 2021, up to the date that financial statements are available to be issued. An entity may elect to apply ASU 2021-01 to eligible hedging relationships existing as of the beginning of the interim period that includes March 12, 2020, and to new eligible hedging relationships entered into after the beginning of the interim period that includes March 12, 2020. The Company does not expect the adoption of ASU 2020-04 to have a material impact on its consolidated financial statements.