PREMISES AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
PREMISES AND EQUIPMENT
Premises and equipment, gross	$ 298,205	$ 305,539
Accumulated depreciation	(137,427)	(144,888)
Premises and equipment, net	160,778	160,651
Land and land improvements
PREMISES AND EQUIPMENT
Premises and equipment, gross	34,487	31,884
Assets held for sale	2,500
Bank premises
PREMISES AND EQUIPMENT
Premises and equipment, gross	158,312	151,724
Bank premises \| Other assets
PREMISES AND EQUIPMENT
Assets held for sale	2,900
Equipment
PREMISES AND EQUIPMENT
Premises and equipment, gross	72,960	85,391
Construction in progress
PREMISES AND EQUIPMENT
Premises and equipment, gross	2,377	4,786
Operating lease right-of-use assets
PREMISES AND EQUIPMENT
Premises and equipment, gross	30,069	$ 31,754
Premises and equipment \| Other assets
PREMISES AND EQUIPMENT
Assets held for sale	$ 5,400

Amount of accumulated depreciation and amortization from plant, property, and equipment and right-of-use asset from operating lease.

No definition available.

+ Details

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Namespace Prefix:	cbu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after accumulated depreciation and amortization, of property, plant, and equipment and operating lease right-of-use asset.

+ References

No definition available.

+ Details

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Namespace Prefix:	cbu_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Amount of assets held-for-sale that are not part of a disposal group.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 15
-Paragraph 4
-Subparagraph (b)(2)
-URI https://asc.fasb.org/extlink&oid=126982154&loc=d3e400-110220

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- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(13))
-URI https://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 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

+ Details

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- References

No definition available.

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- Details

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