v2.4.0.8

LOANS, Allowance For Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Impaired loans [Abstract]
Loans with allowance allocation	$ 1,543		$ 945
Loans without allowance allocation	0		600
Carrying balance	1,543		1,545
Contractual balance	1,851		1,852
Specifically allocated allowance	176		50
Allowance for loan losses [Roll Forward]
Beginning balance	44,319	42,888
Charge-offs	(2,348)	(2,776)
Recoveries	1,226	1,408
Provision	1,000	1,393
Ending balance	44,197	42,913
Consumer Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	8,994	7,070
Charge-offs	(167)	(371)
Recoveries	41	6
Provision	413	587
Ending balance	9,281	7,292
Business Lending [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	17,507	18,013
Charge-offs	(120)	(784)
Recoveries	171	142
Provision	(512)	186
Ending balance	17,046	17,557
Consumer Indirect [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	10,248	9,606
Charge-offs	(1,427)	(891)
Recoveries	796	958
Provision	969	(225)
Ending balance	10,586	9,448
Consumer Direct [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	3,181	3,303
Charge-offs	(492)	(545)
Recoveries	212	298
Provision	186	28
Ending balance	3,087	3,084
Home Equity [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	1,830	1,451
Charge-offs	(129)	(185)
Recoveries	6	4
Provision	111	413
Ending balance	1,818	1,683
Unallocated [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	2,029	2,666
Charge-offs	0	0
Recoveries	0	0
Provision	149	261
Ending balance	2,178	2,927
Acquired Impaired [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	530	779
Charge-offs	(13)	0
Recoveries	0	0
Provision	(316)	143
Ending balance	$ 201	$ 922

X

- Definition

The recorded investment related to impaired financing receivables that have a specific allowance for credit losses.

+ References

No definition available.

+ Details

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

X

- Definition

The recorded investment related to impaired financing receivables that have no specific allowance for credit losses.

+ References

No definition available.

+ Details

Name:	cbu_ImpairedFinancingReceivableWithNoAllowance
Namespace Prefix:	cbu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph d

-Article 9

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

+ References

No definition available.

+ Details

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X

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953550-111524

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X

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524

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X

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524

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X

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph d

-Article 9



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

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X

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 9



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.11)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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