Loans - Narrative (Details)	Sep. 30, 2025 USD ($) loan	Dec. 31, 2024 USD ($) loan	Sep. 30, 2024 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net deferred loan costs	$ 12,837,000	$ 12,457,000	$ 12,266,000
Loans used to collateralize borrowings from the Federal Home Loan Bank of Boston	663,439,000	626,851,000	622,370,000
Loans	$ 2,398,510,000	$ 2,340,940,000	$ 2,307,253,000
Number of mortgage loans in the process of foreclosure \| loan	3	3	2
Mortgage loans in the process of foreclosure	$ 935,000	$ 192,000	$ 127,000
Home Equity Line of Credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of mortgage loans in the process of foreclosure \| loan	1
Mortgage loans in the process of foreclosure	$ 63,000
Asset Pledged as Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	376,592,000	392,562,000	364,068,000
Residential \| Term
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	730,624,000	710,807,000	698,068,000
Interest rate swap agreements \| Designated as Hedging Instrument
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan adjustments	(935,000)	(560,000)	(2,634,000)
Interest rate swap agreements \| Fair Value Hedging \| Designated as Hedging Instrument
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan adjustments	(958,000)	(758,000)	(2,462,000)
Interest rate cap agreements \| Fair Value Hedging \| Designated as Hedging Instrument
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan adjustments	209,000	0	0
Interest rate cap agreements \| Fair Value Hedging \| Designated as Hedging Instrument \| Residential \| Term
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan adjustments	$ (370,000)	$ 0	$ 0

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Amount of fee received for commitment to originate or purchase financing receivable where likelihood of commitment being exercised is remote, to be recognized as service income.

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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