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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

Amount of allowance for credit loss at acquisition date of financing receivable purchased.

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The premium percentage on loans purchased.

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Percentage of allowance for credit loss to total financing receivable outstanding.

+ References

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Amount, after allowance for credit loss, of accrued interest on financing receivable.

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Indicates line item in statement of financial position that includes accrued interest, after allowance for credit loss, on financing receivable.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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The cash outflow for the purchase of loan receivable arising from the financing of goods and services.

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