Fair Value Measurements - Summary of Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financial assets
Securities available for sale	$ 136,253	$ 153,416
Securities held to maturity	784,636	885,586
FHLB of Boston stock	12,321	6,264
Recurring Basis \| Carrying Value
Financial assets
Cash and cash equivalents	25,353	30,719
Securities available for sale	136,253	153,416
Securities held to maturity	980,591	1,051,997
Loans, net	3,989,773	4,025,082
FHLB of Boston stock	12,321	6,264
Accrued interest receivable	15,255	14,118
Mortgage servicing rights	1,511	1,665
Loan level interest rate swaps	59,287	50,784
Risk participation agreements out to counterparties	6	23
Financial liabilities
Deposits, excluding wholesale deposits	4,082,582	4,433,817
Deposits, Wholesale	483,344	381,559
Borrowings	233,905	105,212
Loan level interest rate swaps	59,287	50,784
Risk participation agreements in with counterparties	18	43
Recurring Basis \| Estimated Fair Value
Financial assets
Cash and cash equivalents	25,353	30,719
Securities available for sale	136,253	153,416
Securities held to maturity	784,636	885,586
Loans, net	3,574,502	3,783,051
FHLB of Boston stock	12,321	6,264
Accrued interest receivable	15,255	14,118
Mortgage servicing rights	2,345	2,336
Loan level interest rate swaps	59,287	50,784
Risk participation agreements out to counterparties	6	23
Financial liabilities
Deposits, excluding wholesale deposits	4,078,271	4,429,190
Deposits, Wholesale	483,028	381,505
Borrowings	232,431	105,202
Loan level interest rate swaps	59,287	50,784
Risk participation agreements in with counterparties	18	43
Cash Flow Hedging \| Recurring Basis \| Carrying Value
Financial assets
Interest rate contracts - cash flow hedge	799	1,966
Interest rate contracts - fair value hedge	799	1,966
Cash Flow Hedging \| Recurring Basis \| Estimated Fair Value
Financial assets
Interest rate contracts - cash flow hedge	799	1,966
Interest rate contracts - fair value hedge	799	$ 1,966
Fair Value Hedging \| Recurring Basis
Financial assets
Interest rate contracts - cash flow hedge	6,329
Interest rate contracts - fair value hedge	6,329
Fair Value Hedging \| Recurring Basis \| Estimated Fair Value
Financial assets
Interest rate contracts - cash flow hedge	6,329
Interest rate contracts - fair value hedge	$ 6,329

Interest receivable fair value.

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Loan level interest rate swaps assets fair value disclosure.

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Loan level interest rate swaps liabilities fair value disclosure.

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Risk participation agreements in with counterparties liabilities fair value disclosure.

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Risk participation agreements out to counterparties 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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The aggregate amount of all retail deposit accounts including demand accounts, savings accounts, and certificates of deposit.

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The aggregate amount of all wholesale deposit accounts including certificates of 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 of investment in debt security measured at amortized cost (held-to-maturity).

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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 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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