Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2022
Accounting Policies [Abstract]
Accounting Standards Pending Adoption	Accounting Standards Pending Adoption ASU 2016-13: The FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, as further amended. The ASU requires credit losses on most financial assets measured at amortized cost and certain other instruments to be measured using an expected credit loss model (referred to as the current expected credit loss ("CECL") model). Under this model, entities will estimate credit losses over the entire contractual term of the instrument (considering estimated prepayments, but not expected extensions or modifications unless reasonable expectation of a troubled debt restructuring exists) from the date of initial recognition of that instrument. The ASU also replaces the current accounting model for purchased credit impaired loans and debt securities. The allowance for purchased financial assets with a more-than insignificant amount of credit deterioration since origination ("PCD assets") should be determined in a similar manner to other financial assets measured on an amortized cost basis. However, upon initial recognition, the allowance is added to the purchase price ("gross up approach") to determine the initial amortized cost basis. The subsequent accounting for PCD assets is the same expected loss model described above. Further, the ASU made certain targeted amendments to the existing impairment model for available-for-sale debt securities. For an AFS debt security for which there is neither the intent nor a more-likely-than-not requirement to sell, an entity will record credit losses as an allowance rather than a write-down of the amortized cost basis. Certain incremental disclosures are required. Subsequently, the FASB issued ASU 2018-19, ASU 2019-04, ASU 2019-05, ASU 2019-10, ASU 2019-11, and ASU 2020-02 to clarify, improve, or defer the adoption of ASU 2016-13. In October 2019, the FASB issued ASU 2019-10 which deferred the implementation date of ASU 2016-13 for smaller reporting companies (SRCs) until January 1, 2023. Mid Penn qualified as an SRC as of the most recent measurement date of September 30, 2019; therefore, Mid Penn has chosen to delay the adoption of ASU 2016-13 until January 1, 2023. Mid Penn intends to adopt this ASU effective January 1, 2023. Mid Penn expects that it is probable that total credit loss reserves will increase at the adoption date and that the magnitude of the increase will depend on the composition, characteristics and quality of its loan and lease portfolio and the allowance for debt securities, as well as economic conditions and forecasts at the time of adoption. Mid Penn is conducting parallel runs of its new processes and controls and had begun its model validation process. Mid Penn will continue to make refinements to its credit loss model in advance of the January 1, 2023 adoption date. ASU No. 2022-02: The FASB issued ASU 2022-02, Financial Instruments—Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures. This ASU eliminates the TDR recognition and measurement guidance and, instead, requires that an entity evaluate (consistent with the accounting for other loan modifications) whether a modification represents a new loan or a continuation of an existing loan. In addition, this ASU enhances existing disclosure requirements and introduces new requirements related to certain modifications of receivables made to borrowers experiencing financial difficulty. For public business entities, this ASU requires that an entity disclose current-period gross write-offs by year of origination for financing receivables and net investment in leases within the scope of Subtopic 326-20. Gross write-off information must be included in the vintage disclosures required for public business entities in accordance with paragraph 326-20-50-6, which requires that an entity disclose the amortized cost basis of financing receivables by credit quality indicator and class of financing receivable by year of origination. For entities that have adopted the amendments in update 2016-13, the amendments in this update are effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. For entities that have not yet adopted the amendments in update 2016-13, the effective dates for the amendments in this update are the same as the effective dates in Update 2016-13. The Corporation has not yet adopted this accounting standard as ASU 2016-13 has not been adopted. Management continues to evaluate the impact of its future adoption of this guidance on the Company’s financial statements.
Fair Value Measurement	Fair value measurement and disclosure guidance defines fair value as the price that would be received to sell the asset or transfer the liability in an orderly transaction (that is, not a forced liquidation or distressed sale) between market participants at the measurement date under current market conditions. This guidance provides additional information on determining when the volume and level of activity for the asset or liability has significantly decreased. Information on identifying circumstances when a transaction may not be considered orderly is also included within the guidance. Fair value measurement and disclosure guidance provides a list of factors that a reporting entity should evaluate to determine whether there has been a significant decrease in the volume and level of activity for the asset or liability in relation to normal market activity for the asset or liability. When the reporting entity concludes there has been a significant decrease in the volume and level of activity for the asset or liability, further analysis of the information from that market is needed and significant adjustments to the related prices may be necessary to estimate fair value in accordance with the fair value measurement and disclosure guidance. This guidance clarifies that when there has been a significant decrease in the volume and level of activity for the asset or liability, some transactions may not be orderly. In those situations, the entity must evaluate the weight of the evidence to determine whether the transaction is orderly. The guidance provides a list of circumstances that may indicate that a transaction is not orderly. A transaction price that is not associated with an orderly transaction is given little, if any, weight when estimating fair value. Inputs to valuation techniques refer to the assumptions that market participants would use in measuring the fair value of an asset or liability. Inputs may be observable, meaning those that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources, or unobservable, meaning those that reflect the reporting entity’s own belief about the assumptions market participants would use in pricing the asset or liability based upon the best information available in the circumstances. Fair value measurement and disclosure guidance establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. An asset’s or liability’s placement in the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement or disclosure. The fair value hierarchy is as follows: Level 1 - Inputs that represent quoted prices for identical instruments in active markets. Level 2 - Inputs that represent quoted prices in markets that are not active, or inputs that are observable either directly or indirectly, for substantially the full term of the asset or liability. Level 3 - Inputs that are largely unobservable, as little or no market data exists for the instrument being valued.
Earnings Per Common Share	Earnings Per Common ShareBasic earnings per common share are computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding during each of the periods presented. Diluted earnings per common share are calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding plus common shares that would have been outstanding if dilutive potential common shares, consisting of unvested restricted stock, had been issued. The effect of dilutive unvested restricted stock was not material and did not result in a difference, when rounded to the whole cent, between the basic earnings per share compared to the diluted earnings per share for any of the periods presented.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2022

ASU 2016-13: The FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, as further amended.

The ASU requires credit losses on most financial assets measured at amortized cost and certain other instruments to be measured using an expected credit loss model (referred to as the current expected credit loss ("CECL") model). Under this model, entities will estimate credit losses over the entire contractual term of the instrument (considering estimated prepayments, but not expected extensions or modifications unless reasonable expectation of a troubled debt restructuring exists) from the date of initial recognition of that instrument.

The ASU also replaces the current accounting model for purchased credit impaired loans and debt securities. The allowance for purchased financial assets with a more-than insignificant amount of credit deterioration since origination ("PCD assets") should be determined in a similar manner to other financial assets measured on an amortized cost basis. However, upon initial recognition, the allowance is added to the purchase price ("gross up approach") to determine the initial amortized cost basis. The subsequent accounting for PCD assets is the same expected loss model described above.

Further, the ASU made certain targeted amendments to the existing impairment model for available-for-sale debt securities. For an AFS debt security for which there is neither the intent nor a more-likely-than-not requirement to sell, an entity will record credit losses as an allowance rather than a write-down of the amortized cost basis. Certain incremental disclosures are required.

Subsequently, the FASB issued ASU 2018-19, ASU 2019-04, ASU 2019-05, ASU 2019-10, ASU 2019-11, and ASU 2020-02 to clarify, improve, or defer the adoption of ASU 2016-13.

In October 2019, the FASB issued ASU 2019-10 which deferred the implementation date of ASU 2016-13 for smaller reporting companies (SRCs) until January 1, 2023. Mid Penn qualified as an SRC as of the most recent measurement date of September 30, 2019; therefore, Mid Penn has chosen to delay the adoption of ASU 2016-13 until January 1, 2023.

Mid Penn intends to adopt this ASU effective January 1, 2023. Mid Penn expects that it is probable that total credit loss reserves will increase at the adoption date and that the magnitude of the increase will depend on the composition, characteristics and quality of its loan and lease portfolio and the allowance for debt securities, as well as economic conditions and forecasts at the time of adoption. Mid Penn is conducting parallel runs of its new processes and controls and had begun its model validation process. Mid Penn will continue to make refinements to its credit loss model in advance of the January 1, 2023 adoption date.

ASU No. 2022-02: The FASB issued ASU 2022-02, Financial Instruments—Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures.

This ASU eliminates the TDR recognition and measurement guidance and, instead, requires that an entity evaluate (consistent with the accounting for other loan modifications) whether a modification represents a new loan or a continuation of an existing loan. In addition, this ASU enhances existing disclosure requirements and introduces new requirements related to certain modifications of receivables made to borrowers experiencing financial difficulty.

For public business entities, this ASU requires that an entity disclose current-period gross write-offs by year of origination for financing receivables and net investment in leases within the scope of Subtopic 326-20. Gross write-off information must be included in the vintage disclosures required for public business entities in accordance with paragraph 326-20-50-6, which requires that an entity disclose the amortized cost basis of financing receivables by credit quality indicator and class of financing receivable by year of origination.

For entities that have adopted the amendments in update 2016-13, the amendments in this update are effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. For entities that have not yet adopted the amendments in update 2016-13, the effective dates for the amendments in this update are the same as the effective dates in Update 2016-13. The Corporation has not yet adopted this accounting standard as ASU 2016-13 has not been adopted. Management continues to evaluate the impact of its future adoption of this guidance on the Company’s financial statements.

Fair Value Measurement

Fair value measurement and disclosure guidance defines fair value as the price that would be received to sell the asset or transfer the liability in an orderly transaction (that is, not a forced liquidation or distressed sale) between market participants at the measurement date under current market conditions. This guidance provides additional information on determining when the volume and level of activity for the asset or liability has significantly decreased. Information on identifying circumstances when a transaction may not be considered orderly is also included within the guidance.

Fair value measurement and disclosure guidance provides a list of factors that a reporting entity should evaluate to determine whether there has been a significant decrease in the volume and level of activity for the asset or liability in relation to normal market activity for the asset or liability. When the reporting entity concludes there has been a significant decrease in the volume and level of activity for the asset or liability, further analysis of the information from that market is needed and significant adjustments to the related prices may be necessary to estimate fair value in accordance with the fair value measurement and disclosure guidance.

This guidance clarifies that when there has been a significant decrease in the volume and level of activity for the asset or liability, some transactions may not be orderly. In those situations, the entity must evaluate the weight of the evidence to determine whether the transaction is orderly. The guidance provides a list of circumstances that may indicate that a transaction is not orderly. A transaction price that is not associated with an orderly transaction is given little, if any, weight when estimating fair value.

Inputs to valuation techniques refer to the assumptions that market participants would use in measuring the fair value of an asset or liability. Inputs may be observable, meaning those that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources, or unobservable, meaning those that reflect the reporting entity’s own belief about the assumptions market participants would use in pricing the asset or liability based upon the best information available in the circumstances. Fair value measurement and disclosure guidance establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. An asset’s or liability’s placement in the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement or disclosure. The fair value hierarchy is as follows:

Level 1 - Inputs that represent quoted prices for identical instruments in active markets.

Level 2 - Inputs that represent quoted prices in markets that are not active, or inputs that are observable either directly or indirectly, for substantially the full term of the asset or liability.

Level 3 - Inputs that are largely unobservable, as little or no market data exists for the instrument being valued.

Earnings Per Common Share

Earnings Per Common ShareBasic earnings per common share are computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding during each of the periods presented. Diluted earnings per common share are calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding plus common shares that would have been outstanding if dilutive potential common shares, consisting of unvested restricted stock, had been issued. The effect of dilutive unvested restricted stock was not material and did not result in a difference, when rounded to the whole cent, between the basic earnings per share compared to the diluted earnings per share for any of the periods presented.