Allowance for Loan Losses and Credit Quality - Allocation of Investment in Loans, by Impairment Methodology (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	$ 6,961	$ 4,621
Collectively evaluated for impairment	765,225	766,548
Individually evaluated for impairment	772,186	771,169
Residential real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	1,773	1,782
Collectively evaluated for impairment	224,024	181,384
Individually evaluated for impairment	225,797	183,166
Construction real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	199	210
Collectively evaluated for impairment	73,646	57,207
Individually evaluated for impairment	73,845	57,417
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	4,979	2,422
Collectively evaluated for impairment	317,233	318,205
Individually evaluated for impairment	322,212	320,627
Commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	10	207
Collectively evaluated for impairment	64,146	108,654
Individually evaluated for impairment	64,156	108,861
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	2,614	2,601
Individually evaluated for impairment	2,614	2,601
Municipal
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	83,562	98,497
Individually evaluated for impairment	$ 83,562	$ 98,497

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

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- Definition

Amount excluding accrued interest, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

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The balance of financing receivables that were individually evaluated for impairment.

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