Summary of Significant Accounting Policies - Narrative (Details)		12 Months Ended			27 Months Ended
		Dec. 31, 2023 USD ($) Segment Apartment unit	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2021	Dec. 31, 2020 USD ($)
Number of reportable segments | Segment		1
Cash reserve balances		$ 0	$ 0
Held to maturity, at amortized cost		399,128,000	399,494,000
Held-to-maturity, accrued Interest, after allowance for credit loss		1,900,000
Loan balance		$ 324,500,000	$ 768,500,000
Disposal Group, Not Discontinued Operation, Gain Loss On Disposal, Statement Of Income, Extensible List, Not Disclosed Flag		current operations	current operations
Bank premises and equipment held for sale		$ 974,000	$ 1,300,000
Number of reporting units | unit		1
Goodwill and intangible asset impairment		$ 0	$ 0	$ 0
Finance Lease, Liability, Statement of Financial Position [Extensible List]		Long-term debt	Long-term debt
Decrease in retained earnings		$ (542,350,000)	$ (512,099,000)	(490,076,000)		$ (255,688,000)
Deferred income taxes		24,146,000	13,674,000
Off-balance-sheet credit exposure		3,600,000	85,000
Retained Earnings
Decrease in retained earnings		$ (145,982,000)	(133,114,000)	(91,043,000)		$ (70,175,000)
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses			15,000,000
Decrease in retained earnings	[1]		11,548,000
Deferred income taxes			3,100,000
Off-balance-sheet credit exposure			3,100,000
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Decrease in retained earnings	[1]		11,548,000
Customer Lists Intangible
Core deposit intangible, amortization period		20 years
Enola, Pennsylvania
Carrying value of investment in limited partnership		$ 15,000	58,000
Investment in subsidiaries		$ 15,000	58,000
Dauphin County, Pennsylvania
Number of apartments under the project | Apartment		37
Limited partner capital contribution commitment		$ 7,600,000
Commitment funding term					3 years
Project investment amortization period		10 years
LIHTCs amount awarded for the project		$ 8,500,000
Low income housing tax credit		1,300,000	853,000	853,000
Dauphin County, Pennsylvania | Other Assets
Carrying value of investment in limited partnership		4,500,000	5,200,000
Investment in subsidiaries		4,500,000	5,200,000
Federal Home Loan Bank of Pittsburgh
Other interest and dividend income		864,000	289,000	345,000
Equity securities
Equity securities, fair value		438,000	430,000
Equity securities sold		$ 0	$ 0	$ 0
Maximum | Core Deposit Intangible
Core deposit intangible, amortization period		10 years
Maximum | Building Assets
Property, plant and equipment, useful life		50 years
Maximum | Furniture, fixtures, and equipment
Property, plant and equipment, useful life		10 years
Maximum | Land Improvements
Property, plant and equipment, useful life		20 years
Maximum | Leasehold improvements
Property, plant and equipment, useful life		15 years
Minimum | Building Assets
Property, plant and equipment, useful life		5 years
Minimum | Furniture, fixtures, and equipment
Property, plant and equipment, useful life		3 years
Minimum | Land Improvements
Property, plant and equipment, useful life		10 years
Minimum | Leasehold improvements
Property, plant and equipment, useful life		10 years

[1] The Corporation adopted ASU 2016-13 "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments" effective January 1, 2023. See "Note 1 - Summary of Significant Accounting Policies" for further details.