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Summary of Significant Accounting Policies - Schedule of CECL adoption (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2019 | Dec. 31, 2021 | Oct. 01, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Accounting Standards Update [Extensible List] |  |  | Accounting Standards Update 2016-13 | Accounting Standards Update 2016-13 | Accounting Standards Update 2016-13 |  |  |
Allowance for credit losses on loans | $ 22,874 | [1] | $ 22,113 |  |  | $ 23,023 | [1] |
Allowance for credit losses on unfunded commitments |  |  | 1,697 |  |  |  |  |
Unallocated |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  | 1,265 |  |  |  |  |
Commercial | Commercial and industrial |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 2,530 |  | 2,525 |  |  | 1,709 |  |
Commercial real estate | Commercial real estate, owner-occupied |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 2,778 |  | 3,135 |  |  | 2,776 |  |
Commercial real estate | Commercial real estate, investor-owned |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 12,682 |  | 11,624 |  |  | 12,739 |  |
Commercial real estate | Construction |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 1,557 |  | 860 |  |  | 1,653 |  |
Residential loans | Home equity |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 738 |  | 1,038 |  |  | 595 |  |
Residential loans | Other residential |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 998 |  | 1,260 |  |  | 644 |  |
Consumer loans | Installment and other consumer |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 291 |  | $ 406 |  |  | $ 621 |  |
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans | 748 |  |  |  |  |  |  |
Financing receivable, current expected credit loss, cumulative adjustment on retained earnings, before tax | (1,604) |  |  |  |  |  |  |
Financing receivable, current expected credit loss, cumulative adjustment on retained earnings, tax | 474 |  |  |  |  |  |  |
Financing receivable, current expected credit loss, cumulative adjustment on retained earnings, after tax | (1,130) |  |  |  |  |  |  |
Financing receivable, current expected credit loss, cumulative adjustment on net income, before tax | 856 |  |  |  |  |  |  |
Financing receivable, current expected credit loss, cumulative adjustment on net income, tax | (253) |  |  |  |  |  |  |
Financing receivable, current expected credit loss, cumulative adjustment on net income, after tax | 603 |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment, before tax | 1,082 |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment on retained earnings, before tax | (122) |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment on retained earnings, tax | 36 |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment on retained earnings, after tax | (86) |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment on net income, before tax | (960) |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment on net income, tax | 284 |  |  |  |  |  |  |
Off-balance sheet, credit loss, liability, current expected credit loss, cumulative adjustment on net income, after tax | $ (676) |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | $ 1,604 |  |  |  | $ 23,717
Cumulative Effect, Period of Adoption, Adjustment | Commercial | Commercial and industrial |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | (278) |  |  |  | 2,247
Cumulative Effect, Period of Adoption, Adjustment | Commercial real estate | Commercial real estate, owner-occupied |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | 138 |  |  |  | 3,273
Cumulative Effect, Period of Adoption, Adjustment | Commercial real estate | Commercial real estate, investor-owned |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | 1,755 |  |  |  | 13,379
Cumulative Effect, Period of Adoption, Adjustment | Commercial real estate | Construction |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | 201 |  |  |  | 1,061
Cumulative Effect, Period of Adoption, Adjustment | Residential loans | Home equity |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | (361) |  |  |  | 677
Cumulative Effect, Period of Adoption, Adjustment | Residential loans | Other residential |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | (212) |  |  |  | 1,048
Cumulative Effect, Period of Adoption, Adjustment | Consumer loans | Installment and other consumer |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  | $ (125) |  |  |  | 281
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 1,604
Allowance for credit losses on unfunded commitments |  |  |  |  |  |  |  | 122
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Unallocated |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 486
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Commercial | Commercial and industrial |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | (278)
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Commercial real estate | Commercial real estate, owner-occupied |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 138
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Commercial real estate | Commercial real estate, investor-owned |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 1,755
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Commercial real estate | Construction |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 201
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Residential loans | Home equity |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | (361)
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Residential loans | Other residential |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | (212)
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Consumer loans | Installment and other consumer |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | (125)
Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 23,717
Allowance for credit losses on unfunded commitments |  |  |  |  |  |  |  | 1,819
Cumulative Effect, Period of Adoption, Adjusted Balance | Unallocated |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 1,751
Cumulative Effect, Period of Adoption, Adjusted Balance | Commercial | Commercial and industrial |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 2,247
Cumulative Effect, Period of Adoption, Adjusted Balance | Commercial real estate | Commercial real estate, owner-occupied |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 3,273
Cumulative Effect, Period of Adoption, Adjusted Balance | Commercial real estate | Commercial real estate, investor-owned |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 13,379
Cumulative Effect, Period of Adoption, Adjusted Balance | Commercial real estate | Construction |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 1,061
Cumulative Effect, Period of Adoption, Adjusted Balance | Residential loans | Home equity |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 677
Cumulative Effect, Period of Adoption, Adjusted Balance | Residential loans | Other residential |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | 1,048
Cumulative Effect, Period of Adoption, Adjusted Balance | Consumer loans | Installment and other consumer |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |
Allowance for credit losses on loans |  |  |  |  |  |  |  | $ 281
[1] | Refer to Note 1, Summary of Accounting Policies, for information on the adoption of ASU 2016-13 in 2020.

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