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Allowance for Credit Losses and Credit Quality of Loans, Summary (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2025 | Dec. 31, 2024 | Jun. 30, 2025 | Sep. 30, 2024 | Jun. 30, 2024 | Dec. 31, 2023
Allowance for Credit Losses [Abstract] |  |  |  |  |  |
Allowance for credit losses | $ 139,000 | $ 116,000 | $ 140,200 | $ 119,500 | $ 120,500 | $ 114,400
Percentage of allowance for credit losses | 1.20% | 1.16% |  |  |  |
Loans purchased with credit deterioration |  | $ 0 |  |  |  |
Evans Bancorp, Inc [Member] |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |
Loans purchased with credit deterioration | $ 336,400 |  |  |  |  |
Allowance for credit losses on loans purchased | 7,700 |  |  |  |  |
Allowance for credit losses at acquisition | 20,700 |  |  |  |  |
Evans Bancorp, Inc [Member] | Non-PCD [Member] |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |
Allowance for credit losses at acquisition | 13,000 |  |  |  |  |
Evans Bancorp, Inc [Member] | PCD [Member] |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |
Allowance for credit losses at acquisition | 7,700 |  |  |  |  |
Accrued Interest Receivable [Member] |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |
Allowance for credit losses | 0 | 0 |  |  |  |
AIR on loans | $ 41,800 | $ 34,800 |  |  |  |
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] | Other Assets | Other Assets |  |  |  |
Residential [Member] |  |  |  |  |  |
Allowance for Credit Losses [Abstract] |  |  |  |  |  |
Allowance for credit losses | $ 33,397 | $ 26,560 | $ 33,310 | $ 26,646 | $ 25,874 | $ 22,070
Allowance for credit losses on loans purchased | 145 | 31 |  |  |  |
Amount of loans purchased | $ 13,200 | $ 3,000 |  |  |  |
Premium on loans purchased | 4.70% | 7.00% |  |  |  |

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- Definition Percentage of allowance for credit loss to total financing receivable outstanding. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph a -Subparagraph (1) -Publisher SEC + Details
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- Definition Amount, after allowance for credit loss, of accrued interest on financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-5 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3A -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-3A + Details
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- Definition Amount, excluding accrued interest, of allowance for credit loss at acquisition date of financing receivable purchased with credit deterioration. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-13 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 19 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-19 + Details
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