General	3 Months Ended
Mar. 31, 2018
Accounting Policies [Abstract]
General	General The accompanying unaudited consolidated financial statements of First National Corporation (the Company) and its subsidiary, First Bank (the Bank), have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP. All significant intercompany balances and transactions have been eliminated. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments and reclassifications of a normal and recurring nature considered necessary to present fairly the financial positions at March 31, 2018 and December 31, 2017, the statements of income and comprehensive income for the three months ended March 31, 2018 and 2017 and the cash flows and changes in shareholders’ equity for the three months ended March 31, 2018 and 2017. The statements should be read in conjunction with the consolidated financial statements and related notes included in the Annual Report on Form 10-K for the year ended December 31, 2017. Operating results for the three months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018. Adoption of ASU No. 2014-09, "Revenue from Contracts with Customers: Topic 606." On January 1, 2018, the Company adopted ASU No. 2014-09, "Revenue from Contracts with Customers: Topic 606." This ASU revised guidance for the recognition, measurement, and disclosure of revenue from contracts with customers. The original guidance was amended through subsequent accounting standard updates that resulted in technical corrections, improvements, and a one-year deferral of the effective date to January 1, 2018. The guidance, as amended, is applicable to all entities and replaces significant portions of existing industry and transaction-specific revenue recognition rules with a more principles-based recognition model. Most revenue associated with financial instruments, including interest income, loan origination fees, and credit card fees, is outside the scope of the guidance. Gains and losses on investment securities, derivatives, financial guarantees, and sales of financial instruments are similarly excluded from the scope. The guidance is applicable to noninterest revenue streams such as trust and asset management income, deposit related fees, interchange fees, and merchant income. The Company adopted this guidance via the modified retrospective approach, meaning the standard is applied only to the most current period presented in the financial statements with the cumulative effect of initially applying the standard recognized at the date of initial application. Since the guidance does not apply to revenue associated with financial instruments, including loans and securities that are accounted for under other GAAP, the new guidance did not have a material impact on revenue most closely associated with financial instruments, including interest income and expense. The Company completed its overall assessment of revenue streams and review of related contracts potentially affected by the ASU, including trust and asset management fees, deposit related fees, interchange fees, and merchant income. The Company also completed an evaluation of certain costs related to these revenue streams to determine whether such costs should be presented gross versus net. Based on these assessments, the Company concluded that ASU 2014-09 did not materially change the method in which the Company currently recognizes revenue for these revenue streams. Since there was no net income impact upon adoption of the new guidance, a cumulative effect adjustment to opening retained earnings was not deemed necessary. Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” Among other things, in the amendments in ASU 2016-02, lessees will be required to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (1) A lease liability, which is a lessee‘s obligation to make lease payments arising from a lease, measured on a discounted basis; and (2) A right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. Under the new guidance, lessor accounting is largely unchanged. Certain targeted improvements were made to align, where necessary, lessor accounting with the lessee accounting model and Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application is permitted upon issuance. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. The Company does not expect the adoption of ASU 2016-02 to have a material impact on its consolidated financial statements. The Company has analyzed its current lease commitments, along with reasonable assumptions to project lease activity in future periods, to measure the potential impact on net income and relevant capital and financial ratios. In June 2016, the FASB issued ASU No. 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 amendments in this ASU are effective for SEC filers for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company is currently assessing the impact that ASU 2016-13 will have on its consolidated financial statements. The Company has formed a committee to address the compliance requirements of this ASU and is currently in the process of analyzing gathered data, defining loan pools and segments, and selecting methods for applying the concepts included in this ASU. During 2018, the Company plans to test selected models, build policy and process documentation, and model the impact of the ASU on the capital and strategic plans. This guidance may result in material changes in the Company's accounting for credit losses of financial instruments. In January 2017, the FASB issued ASU No. 2017-04, “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment”. The amendments in this ASU simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Instead, under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. Public business entities that are U.S. Securities and Exchange Commission (SEC) filers should adopt the amendments in this ASU for annual or interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of ASU 2017-04 to have a material impact on its consolidated financial statements. In March 2017, the FASB issued ASU No. 2017-08, “Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities.” The amendments in this ASU shorten the amortization period for certain callable debt securities purchased at a premium. Upon adoption of the standard, premiums on these qualifying callable debt securities will be amortized to the earliest call date. Discounts on purchased debt securities will continue to be accreted to maturity. The amendments are effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. Upon transition, entities should apply the guidance on a modified retrospective basis, with a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption and provide the disclosures required for a change in accounting principle. The Company does not expect the adoption of ASU 2017-08 to have a material impact on its consolidated financial statements. In August 2017, the FASB issued ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” The amendments in this ASU modify the designation and measurement guidance for hedge accounting as well as provide for increased transparency regarding the presentation of economic results on both the financial statements and related footnotes. Certain aspects of hedge effectiveness assessments will also be simplified upon implementation of this update. The amendments are effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2018. Early adoption is permitted, including adoption in any interim period. The Company is currently assessing the impact that ASU 2017-12 will have on its consolidated financial statements. In February 2018, the FASB issued ASU No. 2018-03, “Technical Corrections and Improvements to Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities.” The amendments provide targeted improvements to address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Specifically, the amendments include clarifications related to: measurement elections, transition requirements, and adjustments associated with equity securities without readily determinable fair values; fair value measurement requirements for forward contracts and purchased options on equity securities; presentation requirements for hybrid financial liabilities for which the fair value option has been elected; and measurement requirements for liabilities denominated in a foreign currency for which the fair value option has been elected. The amendments are effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years beginning after June 15, 2018. Early adoption is permitted. The Company does not expect the adoption of ASU 2018-03 to have a material impact on its consolidated financial statements.

General

The accompanying unaudited consolidated financial statements of First National Corporation (the Company) and its subsidiary, First Bank (the Bank), have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information. Accordingly, they do not include all of the information and footnotes required by GAAP. All significant intercompany balances and transactions have been eliminated. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments and reclassifications of a normal and recurring nature considered necessary to present fairly the financial positions at March 31, 2018 and December 31, 2017, the statements of income and comprehensive income for the three months ended March 31, 2018 and 2017 and the cash flows and changes in shareholders’ equity for the three months ended March 31, 2018 and 2017. The statements should be read in conjunction with the consolidated financial statements and related notes included in the Annual Report on Form 10-K for the year ended December 31, 2017. Operating results for the three months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018.

Adoption of ASU No. 2014-09, "Revenue from Contracts with Customers: Topic 606."

On January 1, 2018, the Company adopted ASU No. 2014-09, "Revenue from Contracts with Customers: Topic 606." This ASU revised guidance for the recognition, measurement, and disclosure of revenue from contracts with customers. The original guidance was amended through subsequent accounting standard updates that resulted in technical corrections, improvements, and a one-year deferral of the effective date to January 1, 2018. The guidance, as amended, is applicable to all entities and replaces significant portions of existing industry and transaction-specific revenue recognition rules with a more principles-based recognition model. Most revenue associated with financial instruments, including interest income, loan origination fees, and credit card fees, is outside the scope of the guidance. Gains and losses on investment securities, derivatives, financial guarantees, and sales of financial instruments are similarly excluded from the scope. The guidance is applicable to noninterest revenue streams such as trust and asset management income, deposit related fees, interchange fees, and merchant income. The Company adopted this guidance via the modified retrospective approach, meaning the standard is applied only to the most current period presented in the financial statements with the cumulative effect of initially applying the standard recognized at the date of initial application.

Since the guidance does not apply to revenue associated with financial instruments, including loans and securities that are accounted for under other GAAP, the new guidance did not have a material impact on revenue most closely associated with financial instruments, including interest income and expense. The Company completed its overall assessment of revenue streams and review of related contracts potentially affected by the ASU, including trust and asset management fees, deposit related fees, interchange fees, and merchant income. The Company also completed an evaluation of certain costs related to these revenue streams to determine whether such costs should be presented gross versus net. Based on these assessments, the Company concluded that ASU 2014-09 did not materially change the method in which the Company currently recognizes revenue for these revenue streams. Since there was no net income impact upon adoption of the new guidance, a cumulative effect adjustment to opening retained earnings was not deemed necessary.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842).” Among other things, in the amendments in ASU 2016-02, lessees will be required to recognize the following for all leases (with the exception of short-term leases) at the commencement date: (1) A lease liability, which is a lessee‘s obligation to make lease payments arising from a lease, measured on a discounted basis; and (2) A right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. Under the new guidance, lessor accounting is largely unchanged. Certain targeted improvements were made to align, where necessary, lessor accounting with the lessee accounting model and Topic 606, Revenue from Contracts with Customers. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application is permitted upon issuance. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. The Company does not expect the adoption of ASU 2016-02 to have a material impact on its consolidated financial statements. The Company has analyzed its current lease commitments, along with reasonable assumptions to project lease activity in future periods, to measure the potential impact on net income and relevant capital and financial ratios.

In June 2016, the FASB issued ASU No. 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 amendments in this ASU are effective for SEC filers for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company is currently assessing the impact that ASU 2016-13 will have on its consolidated financial statements. The Company has formed a committee to address the compliance requirements of this ASU and is currently in the process of analyzing gathered data, defining loan pools and segments, and selecting methods for applying the concepts included in this ASU. During 2018, the Company plans to test selected models, build policy and process documentation, and model the impact of the ASU on the capital and strategic plans. This guidance may result in material changes in the Company's accounting for credit losses of financial instruments.

In January 2017, the FASB issued ASU No. 2017-04, “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment”. The amendments in this ASU simplify how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Instead, under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. Public business entities that are U.S. Securities and Exchange Commission (SEC) filers should adopt the amendments in this ASU for annual or interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company does not expect the adoption of ASU 2017-04 to have a material impact on its consolidated financial statements.

In March 2017, the FASB issued ASU No. 2017-08, “Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities.” The amendments in this ASU shorten the amortization period for certain callable debt securities purchased at a premium. Upon adoption of the standard, premiums on these qualifying callable debt securities will be amortized to the earliest call date. Discounts on purchased debt securities will continue to be accreted to maturity. The amendments are effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. Upon transition, entities should apply the guidance on a modified retrospective basis, with a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption and provide the disclosures required for a change in accounting principle. The Company does not expect the adoption of ASU 2017-08 to have a material impact on its consolidated financial statements.

In August 2017, the FASB issued ASU No. 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” The amendments in this ASU modify the designation and measurement guidance for hedge accounting as well as provide for increased transparency regarding the presentation of economic results on both the financial statements and related footnotes. Certain aspects of hedge effectiveness assessments will also be simplified upon implementation of this update. The amendments are effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2018. Early adoption is permitted, including adoption in any interim period. The Company is currently assessing the impact that ASU 2017-12 will have on its consolidated financial statements.

In February 2018, the FASB issued ASU No. 2018-03, “Technical Corrections and Improvements to Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities.” The amendments provide targeted improvements to address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Specifically, the amendments include clarifications related to: measurement elections, transition requirements, and adjustments associated with equity securities without readily determinable fair values; fair value measurement requirements for forward contracts and purchased options on equity securities; presentation requirements for hybrid financial liabilities for which the fair value option has been elected; and measurement requirements for liabilities denominated in a foreign currency for which the fair value option has been elected. The amendments are effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years beginning after June 15, 2018. Early adoption is permitted. The Company does not expect the adoption of ASU 2018-03 to have a material impact on its consolidated financial statements.