Basis of Presentation and Nature of Operations	3 Months Ended
Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Nature of Operations	Basis of Presentation and Nature of Operations ACNB Corporation (the Corporation or ACNB), headquartered in Gettysburg, Pennsylvania, provides banking, insurance, and financial services to businesses and consumers through its wholly-owned subsidiaries, ACNB Bank (Bank) and Russell Insurance Group, Inc. (RIG). The Bank engages in full-service commercial and consumer banking and wealth management services, including trust and retail brokerage, through its twenty-one community banking office locations in Adams, Cumberland, Franklin and York Counties, Pennsylvania. There are also loan production offices situated in Lancaster and York, Pennsylvania, and Hunt Valley, Maryland. RIG is a full-service insurance agency based in Westminster, Maryland, with additional locations in Germantown and Jarrettsville, Maryland. The agency offers a broad range of property and casualty and group life and health insurance to both individual and commercial clients. On July 1, 2017, ACNB completed its acquisition of New Windsor Bancorp, Inc. (New Windsor) of Taneytown, Maryland. At the effective time of the acquisition, New Windsor merged with and into a wholly-owned subsidiary of ACNB, immediately followed by the merger of New Windsor State Bank (NWSB) with and into ACNB Bank. ACNB Bank now operates in the Maryland market as “NWSB Bank, A Division of ACNB Bank” and serves its marketplace with banking and wealth management services via a network of seven community banking offices located in Carroll County, Maryland. On January 11, 2020, ACNB completed its acquisition of Frederick County Bancorp, Inc. (FCBI) and its wholly-owned subsidiary, Frederick County Bank, headquartered in Frederick, Maryland. FCBI was merged with and into a wholly-owned subsidiary of ACNB Corporation immediately followed by the merger of Frederick County Bank with and into ACNB Bank. ACNB Bank now operates in the Frederick County, Maryland, market as “FCB Bank, A Division of ACNB Bank” and serves its marketplace with banking and wealth management services via a network of five community banking offices located in Frederick County, Maryland. Further discussion of the FCBI acquisition can be found in Note 2 of these Notes to Consolidated Financial Statements. The Corporation’s primary sources of revenue are interest income on loans and investment securities and fee income on its products and services. Expenses consist of interest expense on deposits and borrowed funds, provisions for loan losses, and other operating expenses. The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (US GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly ACNB Corporation’s financial position and the results of operations, comprehensive income, changes in stockholders’ equity, and cash flows. All such adjustments are of a normal recurring nature. The accounting policies followed by the Corporation are set forth in Note A to the Corporation’s consolidated financial statements in the 2019 ACNB Corporation Annual Report on Form 10-K, filed with the SEC on March 6, 2020. It is suggested that the consolidated financial statements contained herein be read in conjunction with the consolidated financial statements and notes included in the Corporation’s Annual Report on Form 10-K. The results of operations for the three month period ended March 31, 2020, are not necessarily indicative of the results to be expected for the full year. On January 1, 2019, the Corporation adopted ASU 2016-02, Leases, and all subsequent amendments to the ASU (collectively “Topic 842”). From the lessee’s perspective, the new standard establishes a right-of-use (ROU) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases are classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement for a lessee. Under the optional transition method, only the most recent period presented reflects the adoption of Topic 842 and the comparative prior periods are reported under the previous guidance in Topic 840. The Corporation recorded a $4 million right-of-use asset and lease liability, which represents all of its operating lease commitments, based on the present value of committed lease payments. The ASU offers lessors a practical expedient that mirrors the practical expedient already provided to lessees in ASU 2016-02, Leases (Topic 842). The Corporation adopted the new practical expedient which will allow the Corporation to elect, by class of underlying asset, to not separate nonlease components from the associated lease component when specified conditions are met. Examples of nonlease components include equipment maintenance services, common area maintenance services in real estate, or other goods or services provided to the lessee apart from the right to use the underlying asset. The practical expedient must be applied consistently for all lease contracts. The effect on operations and capital adequacy was not material. On January 1, 2019, the Corporation adopted ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities. The ASU shortens the amortization period for premiums on purchased callable debt securities to the earliest call date (i.e., yield-to-earliest call amortization), rather than amortizing over the full contractual term. The ASU does not change the accounting for securities held at a discount. The amendments apply to callable debt securities with explicit, noncontingent call features that are callable at fixed prices and on preset dates. If a security may be prepaid based upon prepayments of the underlying loans, not because the issuer exercised a date specific call option, it is excluded from the scope of the new standard. However, for instruments with contingent call features, once the contingency is resolved and the security is callable at a fixed price and preset date, the security is within the scope of the amendments. Further, the amendments apply to all premiums on callable debt securities, regardless of how they were generated. The amendments require companies to reset the effective yield using the payment terms of the debt security if the call option is not exercised on the earliest call date. If the security has additional future call dates, any excess of the amortized cost basis over the amount repayable by the issuer at the next call date should be amortized to the next call date. The adoption of this ASU did not have a material effect on the Corporation’s consolidated financial condition or results of operations. The Corporation adopted ASU 2018-09, Codification Improvements. The ASU contains various improvements to various topics in the codification, including clarification that an entity must disclose the required and actual amounts of regulatory capital for each measure of regulatory capital for which the entity must comply. The adoption of this ASU did not impact the Corporation’s consolidated financial condition or results of operations since the Corporation already discloses capital requirements within the Management’s Discussion and Analysis section of this Form 10-Q. The Corporation early adopted ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement. This ASU removes, modifies and adds to existing fair value measurement disclosure requirements. The ASU would be effective for all entities in fiscal years beginning after December 15, 2019, including interim periods, which is first effective for calendar year entities in the March 31, 2020, interim financial statements. In addition, an entity may early adopt any of the removed or modified disclosures immediately and delay adoption of the new disclosures until the effective date. The adoption of this ASU did not have a material effect on the Corporation’s consolidated financial condition or results of operations. The Corporation has evaluated events and transactions occurring subsequent to the balance sheet date of March 31, 2020, for items that should potentially be recognized or disclosed in the consolidated financial statements. The evaluation was conducted through the date these consolidated financial statements were issued. On October 16, 2019, the FASB decided to move forward with finalizing its proposal to defer the effective date for ASU 2016-13 for smaller reporting companies to fiscal years beginning after December 31, 2022, including interim periods within those fiscal periods. Since the Corporation currently meets the SEC definition of a smaller reporting company, the delay will be applicable to the Corporation.

Basis of Presentation and Nature of Operations

ACNB Corporation (the Corporation or ACNB), headquartered in Gettysburg, Pennsylvania, provides banking, insurance, and financial services to businesses and consumers through its wholly-owned subsidiaries, ACNB Bank (Bank) and Russell Insurance Group, Inc. (RIG). The Bank engages in full-service commercial and consumer banking and wealth management services, including trust and retail brokerage, through its twenty-one community banking office locations in Adams, Cumberland, Franklin and York Counties, Pennsylvania. There are also loan production offices situated in Lancaster and York, Pennsylvania, and Hunt Valley, Maryland.

RIG is a full-service insurance agency based in Westminster, Maryland, with additional locations in Germantown and Jarrettsville, Maryland. The agency offers a broad range of property and casualty and group life and health insurance to both individual and commercial clients.

On July 1, 2017, ACNB completed its acquisition of New Windsor Bancorp, Inc. (New Windsor) of Taneytown, Maryland. At the effective time of the acquisition, New Windsor merged with and into a wholly-owned subsidiary of ACNB, immediately followed by the merger of New Windsor State Bank (NWSB) with and into ACNB Bank. ACNB Bank now operates in the Maryland market as “NWSB Bank, A Division of ACNB Bank” and serves its marketplace with banking and wealth management services via a network of seven community banking offices located in Carroll County, Maryland.

On January 11, 2020, ACNB completed its acquisition of Frederick County Bancorp, Inc. (FCBI) and its wholly-owned subsidiary, Frederick County Bank, headquartered in Frederick, Maryland. FCBI was merged with and into a wholly-owned subsidiary of ACNB Corporation immediately followed by the merger of Frederick County Bank with and into ACNB Bank. ACNB Bank now operates in the Frederick County, Maryland, market as “FCB Bank, A Division of ACNB Bank” and serves its marketplace with banking and wealth management services via a network of five community banking offices located in Frederick County, Maryland. Further discussion of the FCBI acquisition can be found in Note 2 of these Notes to Consolidated Financial Statements.

The Corporation’s primary sources of revenue are interest income on loans and investment securities and fee income on its products and services. Expenses consist of interest expense on deposits and borrowed funds, provisions for loan losses, and other operating expenses.

The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (US GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly ACNB Corporation’s financial position and the results of operations, comprehensive income, changes in stockholders’ equity, and cash flows. All such adjustments are of a normal recurring nature.

The accounting policies followed by the Corporation are set forth in Note A to the Corporation’s consolidated financial statements in the 2019 ACNB Corporation Annual Report on Form 10-K, filed with the SEC on March 6, 2020. It is suggested that the consolidated financial statements contained herein be read in conjunction with the consolidated financial statements and notes included in the Corporation’s Annual Report on Form 10-K. The results of operations for the three month period ended March 31, 2020, are not necessarily indicative of the results to be expected for the full year.

On January 1, 2019, the Corporation adopted ASU 2016-02, Leases, and all subsequent amendments to the ASU (collectively “Topic 842”). From the lessee’s perspective, the new standard establishes a right-of-use (ROU) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases are classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement for a lessee. Under the optional transition method, only the most recent period presented reflects the adoption of Topic 842 and the comparative prior periods are reported under the previous guidance in Topic 840. The Corporation recorded a $4 million right-of-use asset and lease liability, which represents all of its operating lease commitments, based on the present value of committed lease payments. The ASU offers lessors a practical expedient that mirrors the practical expedient already provided to lessees in ASU 2016-02, Leases (Topic 842). The Corporation adopted the new practical expedient which will allow the Corporation to elect, by class of underlying asset, to not separate nonlease components from the associated lease component when specified conditions are met. Examples of nonlease components include equipment maintenance services, common area maintenance services in real estate, or other goods or services provided to the lessee apart from the right to use the underlying asset. The practical expedient must be applied consistently for all lease contracts. The effect on operations and capital adequacy was not material.

On January 1, 2019, the Corporation adopted ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities. The ASU shortens the amortization period for premiums on purchased callable debt securities to the earliest call date (i.e., yield-to-earliest call amortization), rather than amortizing over the full contractual term. The ASU does not change the accounting for securities held at a discount. The amendments apply to callable debt securities with explicit, noncontingent call features that are callable at fixed prices and on preset dates. If a security may be prepaid based upon prepayments of the underlying loans, not because the issuer exercised a date specific call option, it is excluded from the scope of the new standard. However, for instruments with contingent call features, once the contingency is resolved and the security is callable at a fixed price and preset date, the security is within the scope of the amendments. Further, the amendments apply to all premiums on callable debt securities, regardless of how they were generated. The amendments require companies to reset the effective yield using the payment terms of the debt security if the call option is not exercised on the earliest call date. If the security has additional future call dates, any excess of the amortized cost basis over the amount repayable by the issuer at the next call date should be amortized to the next call date. The adoption of this ASU did not have a material effect on the Corporation’s consolidated financial condition or results of operations.

The Corporation adopted ASU 2018-09, Codification Improvements. The ASU contains various improvements to various topics in the codification, including clarification that an entity must disclose the required and actual amounts of regulatory capital for each measure of regulatory capital for which the entity must comply. The adoption of this ASU did not impact the Corporation’s consolidated financial condition or results of operations since the Corporation already discloses capital requirements within the Management’s Discussion and Analysis section of this Form 10-Q.

The Corporation early adopted ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement. This ASU removes, modifies and adds to existing fair value measurement disclosure requirements. The ASU would be effective for all entities in fiscal years beginning after December 15, 2019, including interim periods, which is first effective for calendar year entities in the March 31, 2020, interim financial statements. In addition, an entity may early adopt any of the removed or modified disclosures immediately and delay adoption of the new disclosures until the effective date. The adoption of this ASU did not have a material effect on the Corporation’s consolidated financial condition or results of operations.

The Corporation has evaluated events and transactions occurring subsequent to the balance sheet date of March 31, 2020, for items that should potentially be recognized or disclosed in the consolidated financial statements. The evaluation was conducted through the date these consolidated financial statements were issued.

On October 16, 2019, the FASB decided to move forward with finalizing its proposal to defer the effective date for ASU 2016-13 for smaller reporting companies to fiscal years beginning after December 31, 2022, including interim periods within those fiscal periods. Since the Corporation currently meets the SEC definition of a smaller reporting company, the delay will be applicable to the Corporation.