Amount of deposits acquired in an acquisition.

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- Definition

Amount of loans acquired in an acquisition.

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- Definition

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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- Definition

Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

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Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

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 due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties 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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- Definition

The amount of identifiable intangible assets recognized as of the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount of other liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

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- Definition

The amount of property, plant, and equipment recognized as of the acquisition date.

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No definition available.

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

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ACQUISITIONS, Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands				12 Months Ended
	Jan. 04, 2016	Dec. 04, 2015	Jan. 02, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Consideration paid [Abstract]
Cash				$ 575	$ (25,505)	$ 924
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Goodwill				$ 465,142	$ 463,252	$ 375,174
EBS-RMSCO, Inc. [Member]
Consideration paid [Abstract]
Cash			$ 924
Community Bank System, Inc. common stock			0
Total net consideration paid			924
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents			0
Investment securities			0
Loans			0
Premises and equipment			0
Accrued interest receivable			0
Other assets			163
Deposits			0
Other liabilities			0
Total identifiable assets (liabilities), net			741
Goodwill			183
EBS-RMSCO, Inc. [Member] \| Core Deposits [Member]
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Intangibles			0
EBS-RMSCO, Inc. [Member] \| Other Intangibles [Member]
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Intangibles			$ 578
WJL Agencies Inc [Member]
Consideration paid [Abstract]
Cash	$ 575
Community Bank System, Inc. common stock	0
Total net consideration paid	575
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents	0
Investment securities	0
Loans	0
Premises and equipment	0
Accrued interest receivable	0
Other assets	0
Deposits	0
Other liabilities	0
Total identifiable assets (liabilities), net	288
Goodwill	287
WJL Agencies Inc [Member] \| Core Deposits [Member]
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Intangibles	0
WJL Agencies Inc [Member] \| Other Intangibles [Member]
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Intangibles	$ 288
Oneida Financial Corp [Member]
Consideration paid [Abstract]
Cash		$ 56,266
Community Bank System, Inc. common stock		102,202
Total net consideration paid		158,468
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents		81,772
Investment securities		225,729
Loans		399,422
Premises and equipment		22,212
Accrued interest receivable		1,133
Other assets		26,529
Deposits		(699,241)
Other liabilities		(1,333)
Total identifiable assets (liabilities), net		68,787
Goodwill		89,681
Oneida Financial Corp [Member] \| Core Deposits [Member]
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Intangibles		2,570
Oneida Financial Corp [Member] \| Other Intangibles [Member]
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Intangibles		$ 9,994