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Borrowings (Additional Information) (Details) - USD ($) | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Feb. 28, 2021 | Apr. 30, 2006 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2006 | Dec. 31, 2015 | Oct. 08, 2015 | Dec. 31, 2008
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  |  | $ 1,300,000,000 | $ 1,400,000,000 |  |  |  |  |
Line of credit, maximum borrowing capacity |  |  | $ 10,000,000.0 |  |  |  |  |  |
Line of credit, expiration date |  |  | Dec. 17, 2021 |  |  |  |  |  |
Security Owned and Pledged as Collateral, Fair Value |  |  | $ 507,100,000 | 712,400,000 |  |  |  |  |
Securities Sold under Agreements to Repurchase |  |  | 162,439,000 | 237,984,000 |  |  |  |  |
Amortization of Debt Issuance Costs |  |  | 251,000 | 115,000 |  |  |  |  |
Interest on subordinated debentures |  |  | 3,512,000 | 3,266,000 | $ 3,415,000 |  |  |  |
Long-term Line of Credit |  |  | 0 |  |  |  |  |  |
Federal Home Loan Bank Advances |  |  | $ 25,000,000 | 40,825,000 |  |  |  |  |
Debt Instrument, Term |  |  | 10 years |  |  |  |  |  |
Value Of Trust Preferred Securities Included In Tier One Capital |  |  | $ 43,000,000.0 | 43,000,000.0 |  |  | $ 43,000,000.0 |  |
Subordinated Debt |  |  | 59,331,000 | 59,080,000 |  |  | 15,000,000.0 | $ 15,000,000.0 |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Payment for Debt Extinguishment or Debt Prepayment Cost | $ 514,000 |  |  |  |  |  |  |  |
Federal Home Loan Bank Advances [Member] |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Line of credit, maximum borrowing capacity |  |  | 9,900,000 | 9,900,000 |  |  |  |  |
Long-term Line of Credit |  |  | 0 |  |  |  |  |  |
PNC [Member] |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Line of credit, maximum borrowing capacity |  |  | 50,000,000.0 |  |  |  |  |  |
Long-term Line of Credit |  |  | 0 |  |  |  |  |  |
Federal Reserve Bank Advances [Member] |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Line of credit, maximum borrowing capacity |  |  | 54,200,000 |  |  |  |  |  |
Loans Pledged as Collateral |  |  | 80,800,000 |  |  |  |  |  |
Security Owned and Pledged as Collateral, Fair Value |  |  | 4,000 |  |  |  |  |  |
Long-term Line of Credit |  |  | $ 0 |  |  |  |  |  |
Junior Subordinated Debt |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Percentage of trust preferred securities included in Tier I Capital ratio |  |  | 9.60% |  |  |  |  |  |
Value Of Trust Preferred Securities Included In Tier One Capital |  |  | $ 43,000,000.0 |  |  |  |  |  |
Subordinated Debentures [Member] | Subordinated Debt [Member] |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Debt Issuance Costs, Net |  |  | 0 | 251,000 |  |  |  |  |
Long-term borrowings |  |  | 15,000,000 | 14,749,000 |  |  |  |  |
FHLBB Borrowing Maturing March 2025 |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Federal Home Loan Bank Advances |  |  | 25,000,000.0 |  |  |  |  |  |
Tier II Capital [Member] |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Subordinated Debt |  |  | $ 12,000,000.0 | $ 15,000,000.0 |  |  | $ 15,000,000.0 |  |
Subsidiary One [Member] | Junior Subordinated Debt |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms |  | The contract interest rate of the trust preferred securities is three-month LIBOR plus 140 basis points. |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 1.64% | 3.36% |  |  |  |  |
Value of outstanding common shares of subsidiary owned by company |  | $ 1,100,000 |  |  |  |  |  |  |
Proceeds from issuance of trust preferred securities |  | $ 36,100,000 |  |  |  |  |  |  |
Debt interest rate, additional rate over three month LIBOR |  | 14000.00% |  |  |  |  |  |  |
Long-term borrowings |  |  | $ 36,083,000 | $ 36,083,000 |  |  |  |  |
Subsidiary Two [Member] | Junior Subordinated Debt |  |  |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms |  |  |  |  |  | The contract interest rate of the trust preferred securities is the average three-month LIBOR plus 1.42%. |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 1.66% | 3.41% |  |  |  |  |
Value of outstanding common shares of subsidiary owned by company |  |  |  |  |  | $ 248,000 |  |  |
Trust preferred securities assumed in acquisition |  |  |  |  |  |  |  |  | $ 8,000,000.0
Aggregate amount of junior subordinated debt issued to subsidiary by acquired company, prior to acquisition |  |  |  |  |  | $ 8,200,000 |  |  |
Debt Instrument, Term |  |  |  |  |  | 30 years |  |  |
Debt interest rate, additional rate over three month LIBOR |  |  |  |  |  | 142.00% |  |  |
Long-term borrowings |  |  | $ 8,248,000 | $ 8,248,000 |  |  |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5086-111524 + Details
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- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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