Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2020
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. The novel coronavirus (“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 and will likely adversely affect its operations in the further quarters of 2020, 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. The greater the duration and severity of the pandemic, the more likely that estimates will be materially impacted by its effects. 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, 2019. Certain prior period adjustments have been reclassified to conform to the current period presentation.
New Accounting Pronouncements, Policy [Policy Text Block]	*Recently Adopted Accounting Developments* In January 2017, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2017-04, "Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment." ASU 2017-04 simplifies the accounting for goodwill impairment for all entities by requiring impairment charges to be based on the first step in the previous two-step impairment test. Under the new guidance, if a reporting unit’s carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. The standard eliminates the prior requirement to calculate a goodwill impairment charge using Step 2, which requires an entity to calculate any impairment charge by comparing the implied fair value of goodwill with its carrying amount. ASU 2017-04 was effective for the Company on January 1, 2020. The adoption of ASU 2017-04 did not have a material effect on the Company's consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, "Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement." ASU 2018-13 modifies the disclosure requirements on fair value measurements by requiring that Level 3 fair value disclosures include the range and weighted average of significant unobservable inputs used to develop those fair value measurements. For certain unobservable inputs, an entity may disclose other quantitative information in lieu of the weighted average if the entity determines that other quantitative information would be a more reasonable and rational method to reflect the distribution of unobservable inputs used to develop Level 3 fair value measurements. Certain disclosure requirements in Topic 820 were also removed or modified. ASU 2018-13 was effective for the Company on January 1, 2020. The adoption of ASU 2018-13 did not have a material effect on the Company's consolidated financial statements. In March 2020 (revised in April 2020), the federal banking agencies issued an "Interagency Statement on Loan Modifications and Reporting for Financial Institutions Working with Customers Affected by the Coronavirus." This was in response to the COVID-19 pandemic affecting societies and economies around the world. This guidance encourages financial institutions to work prudently with borrowers that may be unable to meet their contractual obligations because of the effects of COVID-19. The guidance explains that, in consultation with the FASB staff, the federal banking agencies have concluded that short-term modifications (e.g. six months) made on a good faith basis to borrowers who were current as of the implementation date of a relief program are not troubled debt restructurings ("TDRs"). The Coronavirus Aid, Relief and Economic Security ("CARES") Act was passed by the U.S. Congress on March 27, 2020. Section 4013 of the CARES Act also addressed COVID-19 related modifications and specified that COVID-19 related modifications on loans that were current as of December 31, 2019 are not TDRs. The Bank implemented a Disaster Assistance Program ("DAP") to provide relief to its borrowers under this guidance. Through June 30, 2020, the Bank had applied this guidance and modified loans to over 729 customers on loan balances of approximately $395 million. As of August 1, 2020, the balance of loans remaining in this program was $219 million or 10.4% of the total portfolio as of that date. The majority of modifications involved three-month deferments of principal and interest. This interagency guidance is expected to have a material impact on the Company's financial statements; however, this impact cannot be quantified at this time. The CARES Act included an allocation of $659 billion for loans to be issued by financial institutions through the Small Business Administration ("SBA"). This program is known as the Paycheck Protection Program ("PPP"). PPP loans are forgivable, in whole or in part, if the proceeds are used for payroll and other permitted purposes in accordance with the requirements of the PPP. These loans carry a fixed rate of 1.00% and a term of two years for all but $2 million which have a five year maturity, if not forgiven, in whole or in part. Payments are deferred for the first six months of the loan. The loans are 100% guaranteed by the SBA. The SBA pays the bank a processing fee ranging from 1% to 5%, based on the size of the loan. The SBA began accepting submissions for these loans on April 3, 2020. As of August 1, 2020, the SBA had approved approximately 2,200 applications submitted by the Bank for loans in excess of $272 million. From a funding perspective, the Bank continues to utilize core funding sources for these loans. 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"), including the Company, 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. The Company will continue to validate its models that will be used upon future adoption of the standard. The implementation of this ASU will likely result in increases to the Company's reserves when implemented. In August 2018, the FASB issued ASU 2018-14, "Compensation-Retirement Benefits-Defined Benefit Plans-General (Subtopic 715-20): Disclosure Framework-Changes to the Disclosure Requirements for Defined Benefit Plans." The amendments in this ASU modify the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. Certain disclosure requirements have been deleted while the following disclosure requirements have been added: the weighted-average interest crediting rates for cash balance plans and other plans with promised interest crediting rates and an explanation of the reasons for significant gains and losses related to changes in the benefit obligation for the period. The amendments also clarify the disclosure requirements in paragraph 715-20-50-3, which state that the following information for defined benefit pension plans should be disclosed: the projected benefit obligation ("PBO") and fair value of plan assets for plans with PBOs in excess of plan assets and the accumulated benefit obligation ("ABO") and fair value of plan assets for plans with ABOs in excess of plan assets. The amendments are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. The Company is currently assessing the impact that ASU 2018-14 will have on its consolidated financial statements. Effective November 25, 2019, the SEC adopted Staff Accounting Bulletin ("SAB") 119. SAB 119 updated portions of SEC interpretative guidance to align with FASB Accounting Standards Codification ("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 December 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes." The ASU is expected to reduce cost and complexity related to the accounting for income taxes by removing specific exceptions to general principles in Topic 740 (eliminating the need for an organization to analyze whether certain exceptions apply in a given period) and improving financial statement preparers' application of certain income tax-related guidance. This ASU is part of the FASB's simplification initiative to make narrow-scope simplifications and improvements to accounting standards through a series of short-term projects. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing the impact that ASU 2019-12 will have on its consolidated financial statements. In January 2020, the FASB issued ASU 2020-01, "Investments - Equity Securities (Topic 321), Investments - Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) - Clarifying the Interactions between Topic 321, Topic 323, and Topic 815." The ASU is based on a consensus of the Emerging Issues Task Force and is expected to increase comparability in accounting for these transactions. ASU 2016-01 made targeted improvements to accounting for financial instruments, including providing an entity the ability to measure certain equity securities without a readily determinable fair value at cost, less any impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Among other topics, the amendments clarify that an entity should consider observable transactions that require it to either apply or discontinue the equity method of accounting. For public business entities, such as the Company, the amendments in the ASU are effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. Early adoption is permitted. The Company does not expect the adoption of ASU 2020-01 to have a material impact on its consolidated financial statements. 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 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. The Company is assessing ASU 2020-04 and its impact on the Company’s transition away from LIBOR for its loan and other financial instruments. On March 12, 2020, the SEC finalized amendments to the definitions of its "accelerated filer" and "large accelerated filer" definitions. The amendments increase the threshold criteria for meeting these filer classifications and are effective on April 27, 2020. Any changes in filer status are to be applied beginning with the filer’s first annual report filed with the SEC subsequent to the effective date. Prior to these changes, the Company was required to comply with section 404(b) of the Sarbanes Oxley Act concerning auditor attestation over internal control over financial reporting as an "accelerated filer" as it had more than $75 million in public float but less than $700 million at the end of the Company’s most recent second quarter. The rule change expands the definition of "smaller reporting companies" to include entities with public float of less than $700 million and less than $100 million in annual revenues. If an entity’s annual revenues exceed $100 million, its category will change back to "accelerated filer". The classifications of "accelerated filer" and "large accelerated filer" require a public company to obtain an auditor attestation concerning the effectiveness of internal control over financial reporting ("ICFR") and include the opinion on ICFR in its annual report on Form 10-K. Smaller reporting companies also have additional time to file quarterly and annual financial statements. All public companies are required to obtain and file annual financial statement audits, as well as provide management’s assertion on effectiveness of ICFR, but the external auditor attestation of ICFR is not required for smaller reporting companies. The Company's annual revenues exceeded $100 million in the previous year, and the Company expects its annual revenues to exceed $100 million in future years and to remain an "accelerated filer." Therefore, this change is not expected to have a significant impact on the Company’s annual reporting and audit requirements.

In January 2017, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2017-04, "Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment." ASU 2017-04 simplifies the accounting for goodwill impairment for all entities by requiring impairment charges to be based on the first step in the previous two-step impairment test. Under the new guidance, if a reporting unit’s carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. The standard eliminates the prior requirement to calculate a goodwill impairment charge using Step 2, which requires an entity to calculate any impairment charge by comparing the implied fair value of goodwill with its carrying amount. ASU 2017-04 was effective for the Company on January 1, 2020. The adoption of ASU 2017-04 did not have a material effect on the Company's consolidated financial statements.

In August 2018, the FASB issued ASU 2018-13, "Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement." ASU 2018-13 modifies the disclosure requirements on fair value measurements by requiring that Level 3 fair value disclosures include the range and weighted average of significant unobservable inputs used to develop those fair value measurements. For certain unobservable inputs, an entity may disclose other quantitative information in lieu of the weighted average if the entity determines that other quantitative information would be a more reasonable and rational method to reflect the distribution of unobservable inputs used to develop Level 3 fair value measurements. Certain disclosure requirements in Topic 820 were also removed or modified. ASU 2018-13 was effective for the Company on January 1, 2020. The adoption of ASU 2018-13 did not have a material effect on the Company's consolidated financial statements.

In March 2020 (revised in April 2020), the federal banking agencies issued an "Interagency Statement on Loan Modifications and Reporting for Financial Institutions Working with Customers Affected by the Coronavirus." This was in response to the COVID-19 pandemic affecting societies and economies around the world. This guidance encourages financial institutions to work prudently with borrowers that may be unable to meet their contractual obligations because of the effects of COVID-19. The guidance explains that, in consultation with the FASB staff, the federal banking agencies have concluded that short-term modifications (e.g. six months) made on a good faith basis to borrowers who were current as of the implementation date of a relief program are not troubled debt restructurings ("TDRs"). The Coronavirus Aid, Relief and Economic Security ("CARES") Act was passed by the U.S. Congress on March 27, 2020. Section 4013 of the CARES Act also addressed COVID-19 related modifications and specified that COVID-19 related modifications on loans that were current as of December 31, 2019 are not TDRs. The Bank implemented a Disaster Assistance Program ("DAP") to provide relief to its borrowers under this guidance. Through June 30, 2020, the Bank had applied this guidance and modified loans to over 729 customers on loan balances of approximately $395 million. As of August 1, 2020, the balance of loans remaining in this program was $219 million or 10.4% of the total portfolio as of that date. The majority of modifications involved three-month deferments of principal and interest. This interagency guidance is expected to have a material impact on the Company's financial statements; however, this impact cannot be quantified at this time.

The CARES Act included an allocation of $659 billion for loans to be issued by financial institutions through the Small Business Administration ("SBA"). This program is known as the Paycheck Protection Program ("PPP"). PPP loans are forgivable, in whole or in part, if the proceeds are used for payroll and other permitted purposes in accordance with the requirements of the PPP. These loans carry a fixed rate of 1.00% and a term of two years for all but $2 million which have a five year maturity, if not forgiven, in whole or in part. Payments are deferred for the first six months of the loan. The loans are 100% guaranteed by the SBA. The SBA pays the bank a processing fee ranging from 1% to 5%, based on the size of the loan. The SBA began accepting submissions for these loans on April 3, 2020. As of August 1, 2020, the SBA had approved approximately 2,200 applications submitted by the Bank for loans in excess of $272 million. From a funding perspective, the Bank continues to utilize core funding sources for these loans.

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"), including the Company, 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. The Company will continue to validate its models that will be used upon future adoption of the standard. The implementation of this ASU will likely result in increases to the Company's reserves when implemented.

In August 2018, the FASB issued ASU 2018-14, "Compensation-Retirement Benefits-Defined Benefit Plans-General (Subtopic 715-20): Disclosure Framework-Changes to the Disclosure Requirements for Defined Benefit Plans." The amendments in this ASU modify the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. Certain disclosure requirements have been deleted while the following disclosure requirements have been added: the weighted-average interest crediting rates for cash balance plans and other plans with promised interest crediting rates and an explanation of the reasons for significant gains and losses related to changes in the benefit obligation for the period. The amendments also clarify the disclosure requirements in paragraph 715-20-50-3, which state that the following information for defined benefit pension plans should be disclosed: the projected benefit obligation ("PBO") and fair value of plan assets for plans with PBOs in excess of plan assets and the accumulated benefit obligation ("ABO") and fair value of plan assets for plans with ABOs in excess of plan assets. The amendments are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. The Company is currently assessing the impact that ASU 2018-14 will have on its consolidated financial statements.

Effective November 25, 2019, the SEC adopted Staff Accounting Bulletin ("SAB") 119. SAB 119 updated portions of SEC interpretative guidance to align with FASB Accounting Standards Codification ("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 December 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes." The ASU is expected to reduce cost and complexity related to the accounting for income taxes by removing specific exceptions to general principles in Topic 740 (eliminating the need for an organization to analyze whether certain exceptions apply in a given period) and improving financial statement preparers' application of certain income tax-related guidance. This ASU is part of the FASB's simplification initiative to make narrow-scope simplifications and improvements to accounting standards through a series of short-term projects. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. Early adoption is permitted. The Company is currently assessing the impact that ASU 2019-12 will have on its consolidated financial statements.

In January 2020, the FASB issued ASU 2020-01, "Investments - Equity Securities (Topic 321), Investments - Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) - Clarifying the Interactions between Topic 321, Topic 323, and Topic 815." The ASU is based on a consensus of the Emerging Issues Task Force and is expected to increase comparability in accounting for these transactions. ASU 2016-01 made targeted improvements to accounting for financial instruments, including providing an entity the ability to measure certain equity securities without a readily determinable fair value at cost, less any impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Among other topics, the amendments clarify that an entity should consider observable transactions that require it to either apply or discontinue the equity method of accounting. For public business entities, such as the Company, the amendments in the ASU are effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. Early adoption is permitted. The Company does not expect the adoption of ASU 2020-01 to have a material impact on its consolidated financial statements.

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 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. The Company is assessing ASU 2020-04 and its impact on the Company’s transition away from LIBOR for its loan and other financial instruments.

On March 12, 2020, the SEC finalized amendments to the definitions of its "accelerated filer" and "large accelerated filer" definitions. The amendments increase the threshold criteria for meeting these filer classifications and are effective on April 27, 2020. Any changes in filer status are to be applied beginning with the filer’s first annual report filed with the SEC subsequent to the effective date. Prior to these changes, the Company was required to comply with section 404(b) of the Sarbanes Oxley Act concerning auditor attestation over internal control over financial reporting as an "accelerated filer" as it had more than $75 million in public float but less than $700 million at the end of the Company’s most recent second quarter. The rule change expands the definition of "smaller reporting companies" to include entities with public float of less than $700 million and less than $100 million in annual revenues. If an entity’s annual revenues exceed $100 million, its category will change back to "accelerated filer". The classifications of "accelerated filer" and "large accelerated filer" require a public company to obtain an auditor attestation concerning the effectiveness of internal control over financial reporting ("ICFR") and include the opinion on ICFR in its annual report on Form 10-K. Smaller reporting companies also have additional time to file quarterly and annual financial statements. All public companies are required to obtain and file annual financial statement audits, as well as provide management’s assertion on effectiveness of ICFR, but the external auditor attestation of ICFR is not required for smaller reporting companies. The Company's annual revenues exceeded $100 million in the previous year, and the Company expects its annual revenues to exceed $100 million in future years and to remain an "accelerated filer." Therefore, this change is not expected to have a significant impact on the Company’s annual reporting and audit requirements.