The threshold balance of financing receivable that is individually evaluated for impairment.

No definition available.

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- Definition

Threshold balance of financing receivables classified as a troubled debt restructuring that are collectively evaluated for impairment.

+ References

No definition available.

+ Details

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Namespace Prefix:	cbu_
Data Type:	xbrli:monetaryItemType
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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524

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Period Type:	duration

- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

+ Details

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LOANS, Troubled Debt Restructuring (TDR) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) Loan	Jun. 30, 2016 USD ($) Loan	Jun. 30, 2017 USD ($) Loan	Jun. 30, 2016 USD ($) Loan	Dec. 31, 2016 USD ($) Loan
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	212		212		214
TDRs, amount	$ 5,989		$ 5,989		$ 5,530
Loans modified in TDR during the year, number \| Loan	13	20	31	35
Loans modified in TDR during the year, amount	$ 486	$ 731	$ 1,176	$ 1,159
Maximum [Member]
Financing Receivable, Modifications [Line Items]
Threshold balance of TDR loans collectively included in general loan loss allocation and qualitative review	$ 500		$ 500
Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	67		67		56
TDRs, amount	$ 2,715		$ 2,715		$ 1,832
Accruing [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	145		145		158
TDRs, amount	$ 3,274		$ 3,274		$ 3,698
Residential Portfolio Segment [Member] \| Consumer Mortgage [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	91		91		81
TDRs, amount	$ 3,885		$ 3,885		$ 3,476
Loans modified in TDR during the year, number \| Loan	1	5	8	8
Loans modified in TDR during the year, amount	$ 43	$ 437	$ 545	$ 652
Residential Portfolio Segment [Member] \| Consumer Mortgage [Member] \| Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	47		47		36
TDRs, amount	$ 2,060		$ 2,060		$ 1,520
Residential Portfolio Segment [Member] \| Consumer Mortgage [Member] \| Accruing [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	44		44		45
TDRs, amount	$ 1,825		$ 1,825		$ 1,956
Commercial Portfolio Segment [Member] \| Minimum [Member]
Financing Receivable, Modifications [Line Items]
Threshold balance of loans individually evaluated for impairment	$ 500		$ 500
Commercial Portfolio Segment [Member] \| Business Lending [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	13		13		11
TDRs, amount	$ 808		$ 808		$ 781
Loans modified in TDR during the year, number \| Loan	3	2	3	2
Loans modified in TDR during the year, amount	$ 363	$ 51	$ 363	$ 51
Commercial Portfolio Segment [Member] \| Business Lending [Member] \| Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	8		8		6
TDRs, amount	$ 416		$ 416		$ 91
Commercial Portfolio Segment [Member] \| Business Lending [Member] \| Accruing [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	5		5		5
TDRs, amount	$ 392		$ 392		$ 690
Consumer Portfolio Segment [Member] \| Consumer Indirect [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	78		78		78
TDRs, amount	$ 774		$ 774		$ 771
Loans modified in TDR during the year, number \| Loan	8	9	14	20
Loans modified in TDR during the year, amount	$ 80	$ 118	$ 156	$ 331
Consumer Portfolio Segment [Member] \| Consumer Indirect [Member] \| Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	0		0		0
TDRs, amount	$ 0		$ 0		$ 0
Consumer Portfolio Segment [Member] \| Consumer Indirect [Member] \| Accruing [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	78		78		78
TDRs, amount	$ 774		$ 774		$ 771
Consumer Portfolio Segment [Member] \| Consumer Direct [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	11		11		23
TDRs, amount	$ 73		$ 73		$ 65
Loans modified in TDR during the year, number \| Loan	1	1	4	1
Loans modified in TDR during the year, amount	$ 0	$ 52	$ 14	$ 52
Consumer Portfolio Segment [Member] \| Consumer Direct [Member] \| Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	0		0		0
TDRs, amount	$ 0		$ 0		$ 0
Consumer Portfolio Segment [Member] \| Consumer Direct [Member] \| Accruing [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	11		11		23
TDRs, amount	$ 73		$ 73		$ 65
Consumer Portfolio Segment [Member] \| Home Equity [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	19		19		21
TDRs, amount	$ 449		$ 449		$ 437
Loans modified in TDR during the year, number \| Loan	0	3	2	4
Loans modified in TDR during the year, amount	$ 0	$ 73	$ 98	$ 73
Consumer Portfolio Segment [Member] \| Home Equity [Member] \| Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	12		12		14
TDRs, amount	$ 239		$ 239		$ 221
Consumer Portfolio Segment [Member] \| Home Equity [Member] \| Accruing [Member]
Financing Receivable, Modifications [Line Items]
TDRs, number \| Loan	7		7		7
TDRs, amount	$ 210		$ 210		$ 216