Summary of Significant Accounting Policies (Narrative) (Details)		3 Months Ended		12 Months Ended		27 Months Ended
	May 04, 2021 USD ($) $ / shares shares	Mar. 31, 2022 USD ($) Apartment shares	Mar. 31, 2021 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2022 USD ($)	Nov. 30, 2021 USD ($)
Loans and leases receivable, net, carrying amount		$ 3,106,384,000		$ 3,089,799,000		$ 3,106,384,000
Loans and leases, net of unearned interest		965,314,000		1,010,039,000		965,314,000
Bank premises and equipment held for sale		3,098,000		3,907,000		3,098,000
Bank premises and equipment held for sale, write off expense		$ 705,000
Asset held for sale, description		Bank premises and equipment designated as held for sale are carried at the lower of cost or market value, and at March 31, 2022 and December 31, 2021, totaled $3,098,000 and $3,907,000, respectively. These balances are related to the December 7, 2021 announcement of a Retail Network Optimization Plan under which the Bank announced its intention to close certain retail locations throughout its expanded footprint. The branch closures occurred on March 4, 2022.  Adjustments to record these held for sale assets at the lower of cost or fair value related to the held for sale properties were included in post-acquisition restructuring expenses and totaled $874,000 for the year ended December 31, 2021. During the three months ended March 31, 2022, Mid Penn had a write-off expense of obsolete bank premises and equipment held for sale of $705,000, as a result of branch closures during the first quarter of 2022, as previously announced on a Form 8-K dated December 7, 2021. There were no impairment charges recorded during the three months ended March 31, 2022 or 2021.
Residential real estate held in other real estate owned		$ 76,000		0		76,000
Foreclosure proceedings in process		697,000		0		697,000
Carrying value of investment in limited partnership		$ 91,000		102,000		91,000
Number of apartments under the project | Apartment		37
Limited partner capital contribution		$ 7,506,000				7,506,000
Limited partner capital contribution, funded period		3 years
Project investment amortization period		10 years
Total LIHTCs amount awarded for the project				8,530,000
Annual LIHTCs amount under the housing project				$ 853,000
Project investment recognition period				10 years
Amortization expense		$ 481,000	$ 281,000
Goodwill		$ 113,835,000		$ 113,835,000		113,835,000
Number of antidilutive shares | shares		0	0
Underwritten Public Offering [Member]
Number of shares issued | shares	2,990,000
Common stock, price per share | $ / shares	$ 25.00
Net proceeds received after underwriting discount and other estimated offering expenses	$ 70,238,000
Aggregate gross proceeds of offering	$ 74,750,000
First Priority Financial Corp. [Member]
Goodwill acquired		$ 39,744,000		39,744,000
Riverview [Member]
Goodwill							$ 50,995,000
Goodwill acquired		50,995,000		50,995,000
Riverview [Member] | Underwritten Public Offering [Member]
Stock issued during period, shares | shares	4,519,776
Riverview [Member] | Rabbi Trust
Benefit plan liabilities related to compensation arrangements		7,447,000		7,708,000		7,447,000
Scottdale Bank and Trust Company [Member]
Goodwill acquired		19,178,000		19,178,000
Phoenix Bancorp Incorporated [Member]
Goodwill acquired		3,918,000		3,918,000
Core Deposit Intangible [Member]
Intangible assets, net		6,199,000		7,282,000		6,199,000
Amortization expense		$ 378,000	$ 272,000
Core Deposit Intangible, Amortization Period		10 years
Impairment of core deposit intangible		$ 0
Increase in core deposit		$ 60,524,000		$ 60,524,000
Finite Lived Intangible Assets Growth Percentage		2.00%		7.00%
Other Assets [Member]
Carrying value of investment in limited partnership		$ 5,774,000		$ 5,962,000		5,774,000
Other Assets [Member] | Riverview [Member] | Rabbi Trust
Cash balance		7,439,000		7,708,000		7,439,000
Non Interest Expense [Member]
Asset held for sale, impairment charge		0		874,000
Reserve for Off-balance Sheet Activities [Member]
Valuation allowances and reserves, balance		$ 74,000		72,000		$ 74,000
Maximum [Member]
Non-residential consumer loans charged off on contractual basis in event of bankruptcy, in period		120 days				120 days
Commercial Portfolio [Member]
Loan terms		1 year
Loan to value ratio		80.00%				80.00%
Residential Portfolio [Member] | Maximum [Member]
Loan terms		30 years
Loan to value ratio		100.00%				100.00%
Loan to value ratio, exposure after private mortgage insurance		85.00%
Small Business Administration [Member] | PPP Loans [Member]
Loans and leases receivable, net, carrying amount		$ 34,124,000		111,286,000		$ 34,124,000
Loan guarantee description		The PPP loans, which are 100 percent guaranteed by the SBA, have up to a five-year term to maturity and carry a low interest rate of 1 percent throughout the loan term.
Nonrefundable loan processing fees received		$ 2,989,000		17,997,000	$ 20,883,000	41,869,000
Deferred loan processing fees		822,000		3,811,000		822,000
Loan processing fees		2,989,000		5,047,000
Loss reserve		$ 0		0
Small Business Administration [Member] | Maximum [Member] | PPP Loans [Member]
Processing fee percentage		5.00%
Small Business Administration [Member] | Minimum [Member] | PPP Loans [Member]
Processing fee percentage		1.00%
Equity Securities [Member]
Equity securities, fair value		$ 474,000		$ 500,000		474,000
Equity Securities [Member] | ASU 2016-01 [Member]
Equity securities, fair value		474,000			$ 500,000	$ 474,000
Equity securities sold		$ 0	$ 0
Home equity lines of credit [Member] | Maximum [Member]
Loan terms		20 years
Loan to value ratio		85.00%				85.00%
Home Equity Lines Of Credit [Member] | Maximum [Member]
Loan terms		10 years