Fair Value Measurements - Summary of Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financial assets
Securities available for sale	$ 188,205	$ 197,803
Securities held to maturity	1,043,391	971,092
FHLB of Boston stock	4,816	4,816
Recurring Basis \| Carrying Value
Financial assets
Cash and cash equivalents	81,748	180,153
Securities available for sale	188,205	197,803
Securities held to maturity	1,115,824	977,061
Loans, net	3,383,103	3,284,610
Loans held for sale	918	1,490
FHLB of Boston stock	4,816	4,816
Accrued interest receivable	9,718	9,162
Mortgage servicing rights	1,063	1,083
Interest rate contracts	1,133	3,513
Loan level interest rate swaps	23,110	23,431
Risk participation agreements out to counterparties	76	107
Financial liabilities
Deposits	4,473,735	4,331,152
Borrowings	16,140	16,510
Loan level interest rate swaps	23,110	23,431
Risk participation agreements in with counterparties	186	293
Recurring Basis \| Estimated Fair Value
Financial assets
Cash and cash equivalents	81,748	180,153
Securities available for sale	188,205	197,803
Securities held to maturity	1,043,391	971,092
Loans, net	3,317,481	3,230,339
Loans held for sale	918	1,528
FHLB of Boston stock	4,816	4,816
Accrued interest receivable	9,718	9,162
Mortgage servicing rights	1,602	1,518
Interest rate contracts	1,133	3,513
Loan level interest rate swaps	23,110	23,431
Risk participation agreements out to counterparties	76	107
Financial liabilities
Deposits	4,472,404	4,330,991
Borrowings	16,144	16,523
Loan level interest rate swaps	23,110	23,431
Risk participation agreements in with counterparties	$ 186	$ 293

Interest receivable fair value.

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Loan level interest rate swaps assets fair value disclosure.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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