Amount of deposits acquired in an acquisition.

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Amount of loans acquired in an acquisition.

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Refers to the number of branch locations added upon merger.

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The number of counties where the bank operates or has branches.

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The number of new counties where the bank has extended its footprints.

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Number of shares of equity interests issued or issuable to acquire entity.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of assets acquired at the acquisition date.

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Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of addition (reduction) to the amount at which a liability could be incurred (settled) in a current transaction between willing parties.

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Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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ACQUISITIONS (Narrative) (Details) shares in Thousands, $ in Thousands		3 Months Ended	12 Months Ended
	Jun. 12, 2020 USD ($) country Office shares	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Acquisitions [Abstract]
Goodwill		$ 793,456	$ 793,708	$ 773,473
Steuben Trust Corporation [Member]
Acquisitions [Abstract]
Cash	$ 21,600		21,613
Issuance of common shares (in shares) \| shares	1,360
Purchase price of acquisition	$ 98,600		98,555
Deposits	516,300		516,274
Goodwill	20,000		19,983
Assets acquired	607,800
Loans	339,700		339,017
Investment securities	$ 180,500		$ 180,497
Revenue earned		1,300
Direct expenses		3,200
Increase (decrease) in other liabilities as a result of reclassification and adjustment		300
Increase (decrease) in goodwill as a result of fair value adjustment		$ 300
Steuben Trust Corporation [Member] \| Western New York State [Member]
Acquisitions [Abstract]
Number of counties where the bank has facilities \| country	4
Number of new counties where the bank has extended footprints \| country	2
Number of branch locations \| Office	11