Fair Value Measurements - Summary of Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial assets
Securities available for sale	$ 153,053	$ 168,163
Securities held to maturity	291,993	281,310
FHLB Boston stock	8,245	6,844
Recurring Basis \| Carrying Value
Financial assets
Cash and cash equivalents	38,557	18,473
Securities available for sale	153,053	168,163
Securities held to maturity	286,350	282,869
Loans, net	2,079,451	1,543,004
Loans held for sale	384
FHLB Boston stock	8,245	6,844
Accrued interest receivable	7,485	5,762
Mortgage servicing rights	891	666
Interest rate contracts	3,528	1,970
Loan level interest rate swaps	12,348	5,782
Risk participation agreements out to counterparties	46	28
Financial liabilities
Deposits	2,329,665	1,811,410
Short-term borrowings	103,000	90,000
Long-term borrowings	3,323	3,409
Loan level interest rate swaps	12,348	5,782
Risk participation agreements in with counterparties	459	179
Recurring Basis \| Estimated Fair Value
Financial assets
Cash and cash equivalents	38,557	18,473
Securities available for sale	153,053	168,163
Securities held to maturity	291,993	281,310
Loans, net	2,036,666	1,484,905
Loans held for sale	384
FHLB Boston stock	8,245	6,844
Accrued interest receivable	7,485	5,762
Mortgage servicing rights	1,105	941
Interest rate contracts	3,528	1,970
Loan level interest rate swaps	12,348	5,782
Risk participation agreements out to counterparties	46	28
Financial liabilities
Deposits	2,328,568	1,809,051
Short-term borrowings	103,031	90,000
Long-term borrowings	3,316	3,363
Loan level interest rate swaps	12,348	5,782
Risk participation agreements in with counterparties	$ 459	$ 179

Interest receivable fair value.

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- Definition

Loan level interest rate swaps assets fair value disclosure.

+ References

No definition available.

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Loan level interest rate swaps liabilities fair value disclosure.

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- Definition

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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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
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- Definition

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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No definition available.

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- Definition

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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-SubTopic 325
-Section 45
-Paragraph 1
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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 5
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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
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-Paragraph 2
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-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

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