Basis of Presentation (Policy)	9 Months Ended
Sep. 30, 2017
Basis of Presentation [Abstract]
Principles of Consolidation	The accompanying unaudited consolidated financial statements of DNB Financial Corporation (referred to herein as the "Corporation" or "DNB") and its subsidiary, DNB First, National Association (the "Bank") have been prepared in accordance with the instructions for Form 10-Q and therefore do not include certain information or footnotes necessary for the presentation of financial condition, statement of operations and statement of cash flows required by generally accepted accounting principles. However, in the opinion of management, the consolidated financial statements reflect all adjustments (which consist of normal recurring adjustments) necessary for a fair presentation of the results for the unaudited periods. Prior amounts not affecting net income are reclassified when necessary to conform to current period classifications. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results which may be expected for the entire year. The consolidated financial statements should be read in conjunction with the Annual Report and report on Form 10-K for the year ended December 31, 2016.
Subsequent Events	Subsequent Events-- Management has evaluated events and transactions occurring subsequent to September 30, 2017 for items that should potentially be recognized or disclosed in these Consolidated Financial Statements. The evaluation was conducted through the date these financial statements were issued.
Recent Accounting Pronouncements	Recent Accounting Pronouncements- Accounting Developments Affecting DNB In May 2014, the FASB issued ASU No. 2014-09, ‘‘Revenue from Contracts with Customers (Topic 606).’’ The updated standard is a new comprehensive revenue recognition model that requires revenue to be recognized in a manner that depicts the transfer of goods or services to a customer at an amount that reflects the consideration expected to be received in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14 which deferred the effective date of ASU 2014-09 by one year. During 2016 and 2017, the FASB issued ASU Nos. 2016-10, 2016-12, 2016-20, and 2017-13 that provides additional guidance related to the identification of performance obligations within a contract, assessing collectability, contract costs, and other technical corrections and improvements. ASU 2014-09 will become effective for the Company for the annual period beginning after December 15, 2017, and for interim periods within the annual period. ASU 2014-09 allows for either full retrospective or modified retrospective adoption. DNB is determining the anticipated effects of these ASUs on the Consolidated Financial Statements and related disclosures. Interest income on the Consolidated Statement of Operations is excluded from the scope of ASU 2014-09. DNB is in the process of evaluating non-interest income on the Consolidated Statement of Operations to determine if the revenue streams are in the scope of the new standards, and to analyze the effect of any differences expected with implementation. DNB’s process of analyzing non-interest income revenue streams will include the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The evaluation of non-interest income revenue streams includes service charges on deposit accounts, card fees, other charges and fees, investment banking income, trust and investment, retail investment services, and other income. The Company also continues to evaluate the related changes to disclosures that may be required, which are expected to be significant. Based on the principal versus agent guidance included within the new standards, reclassifications will be made to net certain expenses and revenue for DNB Investment Management and Trust services. These reclassifications are not expected to affect net income. Otherwise, DNB’s continuing evaluation has not identified significant expected changes to the recognition of revenue at this time. DNB plans to adopt the standards beginning January 1, 2018 and expects to use the modified retrospective method of adoption. Although the new revenue standards are not expected to have a significant impact on our prior year or ongoing net income, changes to our processes related to revenue recognition and the control activities within them will be implemented effective January 1, 2018. This includes the development of new controls based on the five-step model in the standards and gathering of information required for disclosures. DNB’s revenue has been more significantly weighted towards net interest income on financial assets and liabilities, which is explicitly excluded from the scope of the new standard. DNB is continuing to assess its revenue streams and reviewing its contracts with customers that are potentially affected by the new guidance including wealth and asset management revenue, fees on deposits, gains and losses on the sale of other real estate owned, credit and debit card interchange fees. DNB adopted ASU 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement Period Adjustments on a prospective basis. This amendment eliminates the requirement to account for adjustments to provisional amounts recognized in a business combination retrospectively. Instead, the acquirer will recognize the adjustments to provisional amounts during the period in which the adjustments are determined, including the effect on earnings of any amounts the acquirer would have recorded in previous periods if the accounting had been completed at the acquisition date. DNB evaluated the impact of this guidance and does not anticipate a material impact to the consolidated financial statements at this time. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Subtopic 825-10) – Recognition and Measurement of Financial Assets and Financial Liabilities. The guidance addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. In particular, the guidance revises an entity’s accounting related to (1) the classification and measurement of investments in equity securities and (2) the presentation of certain fair value changes for financial liabilities measured at fair value. The guidance also amends certain disclosure requirements associated with fair value of financial instruments. For public business entities, the guidance is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Entities should apply the amendments by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. As of September 30, 2017, DNB did not hold any equity investments (excluding restricted investments in bank stocks). DNB does not expect to make significant purchases of equity investments; therefore, the adoption of this ASU is not expected to be material to DNB's consolidated financial statements. In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases. 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 will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. A modified retrospective transition approach is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. DNB has determined that upon the adoption of ASU 2016-02 we will be required to recognize a right-of-use asset and a corresponding liability based on the then present value of such obligation. DNB has not yet determined the impact ASU 2016-02 will have on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, "Improvements to Employee Share-Based Payment Accounting." This ASU simplifies several aspects of the accounting for employee share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. For public business entities, this ASU is effective for financial statements issued for fiscal years beginning after December 15, 2016, and interim periods therein. Accordingly, effective January of 2017, DNB adopted the pronouncement. The adoption of this pronouncement was immaterial to DNB’s consolidated financial statements. During the three and nine month periods ended September 30, 2017, DNB had a $2,000 and $155,000 tax benefit for stock option exercises, respectively. In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments," (ASU 2016-13), which addresses concerns regarding the perceived delay in recognition of credit losses under the existing incurred loss model. The amendment introduces a new, single model for recognizing credit losses on all financial instruments presented on cost basis. Under the new model, entities must estimate current expected credit losses by considering all available relevant information, including historical and current information, as well as reasonable and supportable forecasts of future events. The update also requires additional qualitative and quantitative information to allow users to better understand the credit risk within the portfolio and the methodologies for determining allowance. ASU 2016-13 is effective for DNB on January 1, 2020 and must be applied using the modified retrospective approach with limited exceptions. Early adoption is permitted. While DNB is currently in the process of evaluating the impact of the amended guidance on its consolidated financial statements, it currently expects the ALLL to increase upon adoption given that the allowance will be required to cover the full remaining expected life of the portfolio upon adoption, rather than the incurred loss model under current U.S. GAAP. The extent of this increase is still being evaluated and will depend on economic conditions and the composition of DNB’s loan portfolio at the time of adoption. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230). The amendments in this update provide guidance for eight specific cash flow classification issues for which current guidance is unclear or does not exist, thereby reducing diversity in practice. For public companies, the update is effective for annual periods beginning after December 15, 2017. DNB is currently evaluating this ASU, particularly related to cash payments for debt prepayment costs and cash proceeds received from the settlement of BOLI policies as these areas might affect DNB in the future. This ASU, however, is not expected to have a material impact on DNB's consolidated financial statements because the guidance only affects the classification within the statement of cash flows. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805), Clarifying the Definition of a Business. The new guidance narrows the existing definition of a business and provides a framework for evaluating whether a transaction should be accounted for as an acquisition (or disposal) of assets or a business. The guidance requires an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets; if so, the set of transferred assets and activities (collectively, the set) is not a business. To be considered a business, the set would need to include an input and a substantive process that together significantly contribute to the ability to create outputs, as defined by the ASU. The guidance is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and should be applied prospectively. Early adoption is permitted. DNB will apply this guidance to applicable transactions after the adoption date. In January 2017, the Financial Accounting Standards Board (“FASB”) issued ASU 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The ASU simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Instead, under the amendments, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with its carrying amount. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount when measuring the goodwill impairment loss, if applicable. The update also eliminated the requirements for zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. The amendments are effective for public business entities for its annual or any 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. DNB will not early adopt this ASU for its annual goodwill impairment test, and will conduct a qualitative test (step zero) as of October 1, 2017. The adoption of this ASU is not expected to have a material impact on DNB’s consolidated financial statements. In March 2017, the FASB issued ASU No. 2017-07, “Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” Under the new guidance, employers will present the service cost component of the net periodic benefit cost in the same income statement line item (e.g., Salaries and Benefits) as other employee compensation costs arising from services rendered during the period. In addition, only the service cost component will be eligible for capitalization in assets. Employers will present the other components separately (e.g., Other Noninterest Expense) from the line item that includes the service cost. ASU No. 2017-07 is effective for interim and annual reporting periods beginning after December 15, 2017. Early adoption is permitted, however, DNB has decided not to early adopt. Employers will apply the guidance on the presentation of the components of net periodic benefit cost in the income statement retrospectively. ASU No. 2017-07 is not expected to have a material impact on DNB Consolidated Financial Statements because the Pension plan has been frozen to new accruals since December 31, 2003, and thus, generated no service cost in any subsequent year). In March of 2017, the FASB issued ASU No. 2017-08, “Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities” (“ASU 2017-08”). This guidance shortens the amortization period for premiums on certain callable debt securities to the earliest call date (with an explicit, non-contingent call feature that is callable at a fixed price and on a preset dates), rather than contractual maturity date as currently required under GAAP. The ASU does not impact instruments without preset call dates such as mortgage-backed securities. 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 ASU. ASU 2017-08 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, and early adoption is permitted. Accordingly, effective January of 2017, DNB early adopted the pronouncement. DNB’s current accounting treatment is consistent with the provisions in ASU-2017-08. As a result, there was no impact to the consolidated financial statements.

Recent Accounting Pronouncements-

Accounting Developments Affecting DNB

In May 2014, the FASB issued ASU No. 2014-09, ‘‘Revenue from Contracts with Customers (Topic 606).’’ The updated standard is a new comprehensive revenue recognition model that requires revenue to be recognized in a manner that depicts the transfer of goods or services to a customer at an amount that reflects the consideration expected to be received in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14 which deferred the effective date of ASU 2014-09 by one year. During 2016 and 2017, the FASB issued ASU Nos. 2016-10, 2016-12, 2016-20, and 2017-13 that provides additional guidance related to the identification of performance obligations within a contract, assessing collectability, contract costs, and other technical corrections and improvements. ASU 2014-09 will become effective for the Company for the annual period beginning after December 15, 2017, and for interim periods within the annual period. ASU 2014-09 allows for either full retrospective or modified retrospective adoption.

DNB is determining the anticipated effects of these ASUs on the Consolidated Financial Statements and related disclosures. Interest income on the Consolidated Statement of Operations is excluded from the scope of ASU 2014-09. DNB is in the process of evaluating non-interest income on the Consolidated Statement of Operations to determine if the revenue streams are in the scope of the new standards, and to analyze the effect of any differences expected with implementation. DNB’s process of analyzing non-interest income revenue streams will include the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The evaluation of non-interest income revenue streams includes service charges on deposit accounts, card fees, other charges and fees, investment banking income, trust and investment, retail investment services, and other income. The Company also continues to evaluate the related changes to disclosures that may be required, which are expected to be significant. Based on the principal versus agent guidance included within the new standards, reclassifications will be made to net certain expenses and revenue for DNB Investment Management and Trust services. These reclassifications are not expected to affect net income. Otherwise, DNB’s continuing evaluation has not identified significant expected changes to the recognition of revenue at this time.

DNB plans to adopt the standards beginning January 1, 2018 and expects to use the modified retrospective method of adoption. Although the new revenue standards are not expected to have a significant impact on our prior year or ongoing net income, changes to our processes related to revenue recognition and the control activities within them will be implemented effective January 1, 2018. This includes the development of new controls based on the five-step model in the standards and gathering of information required for disclosures. DNB’s revenue has been more significantly weighted towards net interest income on financial assets and liabilities, which is explicitly excluded from the scope of the new standard. DNB is continuing to assess its revenue streams and reviewing its contracts with customers that are potentially affected by the new guidance including wealth and asset management revenue, fees on deposits, gains and losses on the sale of other real estate owned, credit and debit card interchange fees.

DNB adopted ASU 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement Period Adjustments on a prospective basis. This amendment eliminates the requirement to account for adjustments to provisional amounts recognized in a business combination retrospectively. Instead, the acquirer will recognize the adjustments to provisional amounts during the period in which the adjustments are determined, including the effect on earnings of any amounts the acquirer would have recorded in previous periods if the accounting had been completed at the acquisition date. DNB evaluated the impact of this guidance and does not anticipate a material impact to the consolidated financial statements at this time.

In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments – Overall (Subtopic 825-10) – Recognition and Measurement of Financial Assets and Financial Liabilities. The guidance addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. In particular, the guidance revises an entity’s accounting related to (1) the classification and measurement of investments in equity securities and (2) the presentation of certain fair value changes for financial liabilities measured at fair value. The guidance also amends certain disclosure requirements associated with fair value of financial instruments. For public business entities, the guidance is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Entities should apply the amendments by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. As of September 30, 2017, DNB did not hold any equity investments (excluding restricted investments in bank stocks). DNB does not expect to make significant purchases of equity investments; therefore, the adoption of this ASU is not expected to be material to DNB's consolidated financial statements.

In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases. 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 will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. A modified retrospective transition approach is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. DNB has determined that upon the adoption of ASU 2016-02 we will be required to recognize a right-of-use asset and a corresponding liability based on the then present value of such obligation. DNB has not yet determined the impact ASU 2016-02 will have on its consolidated financial statements.

In March 2016, the FASB issued ASU 2016-09, "Improvements to Employee Share-Based Payment Accounting." This ASU simplifies several aspects of the accounting for employee share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. For public business entities, this ASU is effective for financial statements issued for fiscal years beginning after December 15, 2016, and interim periods therein. Accordingly, effective January of 2017, DNB adopted the pronouncement. The adoption of this pronouncement was immaterial to DNB’s consolidated financial statements. During the three and nine month periods ended September 30, 2017, DNB had a $2,000 and $155,000 tax benefit for stock option exercises, respectively.

In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments," (ASU 2016-13), which addresses concerns regarding the perceived delay in recognition of credit losses under the existing incurred loss model. The amendment introduces a new, single model for recognizing credit losses on all financial instruments presented on cost basis. Under the new model, entities must estimate current expected credit losses by considering all available relevant information, including historical and current information, as well as reasonable and supportable forecasts of future events. The update also requires additional qualitative and quantitative information to allow users to better understand the credit risk within the portfolio and the methodologies for determining allowance. ASU 2016-13 is effective for DNB on January 1, 2020 and must be applied using the modified retrospective approach with limited exceptions. Early adoption is permitted. While DNB is currently in the process of evaluating the impact of the amended guidance on its consolidated financial statements, it currently expects the ALLL to increase upon adoption given that the allowance will be required to cover the full remaining expected life of the portfolio upon adoption, rather than the incurred loss model under current U.S. GAAP. The extent of this increase is still being evaluated and will depend on economic conditions and the composition of DNB’s loan portfolio at the time of adoption.

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230). The amendments in this update provide guidance for eight specific cash flow classification issues for which current guidance is unclear or does not exist, thereby reducing diversity in practice. For public companies, the update is effective for annual periods beginning after December 15, 2017. DNB is currently evaluating this ASU, particularly related to cash payments for debt prepayment costs and cash proceeds received from the settlement of BOLI policies as these areas might affect DNB in the future. This ASU, however, is not expected to have a material impact on DNB's consolidated financial statements because the guidance only affects the classification within the statement of cash flows.

In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805), Clarifying the Definition of a Business. The new guidance narrows the existing definition of a business and provides a framework for evaluating whether a transaction should be accounted for as an acquisition (or disposal) of assets or a business. The guidance requires an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets; if so, the set of transferred assets and activities (collectively, the set) is not a business. To be considered a business, the set would need to include an input and a substantive process that together significantly contribute to the ability to create outputs, as defined by the ASU. The guidance is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and should be applied prospectively. Early adoption is permitted. DNB will apply this guidance to applicable transactions after the adoption date.

In January 2017, the Financial Accounting Standards Board (“FASB”) issued ASU 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The ASU simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Instead, under the amendments, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value with its carrying amount. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount when measuring the goodwill impairment loss, if applicable. The update also eliminated the requirements for zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. The amendments are effective for public business entities for its annual or any 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. DNB will not early adopt this ASU for its annual goodwill impairment test, and will conduct a qualitative test (step zero) as of October 1, 2017. The adoption of this ASU is not expected to have a material impact on DNB’s consolidated financial statements.

In March 2017, the FASB issued ASU No. 2017-07, “Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” Under the new guidance, employers will present the service cost component of the net periodic benefit cost in the same income statement line item (e.g., Salaries and Benefits) as other employee compensation costs arising from services rendered during the period. In addition, only the service cost component will be eligible for capitalization in assets. Employers will present the other components separately (e.g., Other Noninterest Expense) from the line item that includes the service cost. ASU No. 2017-07 is effective for interim and annual reporting periods beginning after December 15, 2017. Early adoption is permitted, however, DNB has decided not to early adopt. Employers will apply the guidance on the presentation of the components of net periodic benefit cost in the income statement retrospectively. ASU No. 2017-07 is not expected to have a material impact on DNB Consolidated Financial Statements because the Pension plan has been frozen to new accruals since December 31, 2003, and thus, generated no service cost in any subsequent year).

In March of 2017, the FASB issued ASU No. 2017-08, “Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities” (“ASU 2017-08”). This guidance shortens the amortization period for premiums on certain callable debt securities to the earliest call date (with an explicit, non-contingent call feature that is callable at a fixed price and on a preset dates), rather than contractual maturity date as currently required under GAAP. The ASU does not impact instruments without preset call dates such as mortgage-backed securities. 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 ASU. ASU 2017-08 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, and early adoption is permitted. Accordingly, effective January of 2017, DNB early adopted the pronouncement. DNB’s current accounting treatment is consistent with the provisions in ASU-2017-08. As a result, there was no impact to the consolidated financial statements.