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LOANS, Loan Summary (Details) (USD $) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Loans receivable, net [Abstract] |  |  |
Gross loans, including deferred origination costs | $ 4,236,206,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount | $ 4,109,083,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount |
Allowance for loan losses | (45,341,000)us-gaap_LoansAndLeasesReceivableAllowance | (44,319,000)us-gaap_LoansAndLeasesReceivableAllowance | (42,888,000)us-gaap_LoansAndLeasesReceivableAllowance
Net loans | 4,190,865,000 us-gaap_LoansAndLeasesReceivableNetReportedAmount | 4,064,764,000 us-gaap_LoansAndLeasesReceivableNetReportedAmount |
Net deferred loan origination costs | 18,700,000 us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums | 18,500,000 us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums |
Loans receivable, related parties [Roll Forward] |  |  |
Balance at beginning of year | 9,448,000 us-gaap_LoansAndLeasesReceivableRelatedParties | 8,292,000 us-gaap_LoansAndLeasesReceivableRelatedParties |
New loans | 1,647,000 us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions | 3,643,000 us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions |
Payments | (2,167,000)us-gaap_LoansAndLeasesReceivableRelatedPartiesCollections | (2,487,000)us-gaap_LoansAndLeasesReceivableRelatedPartiesCollections |
Balance at end of year | 8,928,000 us-gaap_LoansAndLeasesReceivableRelatedParties | 9,448,000 us-gaap_LoansAndLeasesReceivableRelatedParties |
Credit impaired acquired loans [Abstract] |  |  |
Outstanding principal balance | 5,957,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingPrincipalBalance | 11,457,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingPrincipalBalance |
Carrying amount | 5,312,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentCarryingAmountNet | 7,090,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentCarryingAmountNet |
Credit impaired acquired loans, total balance due | 6,100,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingBalance | 13,100,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingBalance |
Non-impaired acquired loans [Abstract] |  |  |
Outstanding principal balance | 276,584,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairmentOutstandingBalance | 342,542,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairmentOutstandingBalance |
Carrying amount | 267,496,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairedCarryingAmountNet | 330,118,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairedCarryingAmountNet |
Total acquired loans [Abstract] |  |  |
Outstanding principal balance | 282,541,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedOutstandingBalance | 353,999,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedOutstandingBalance |
Carrying amount | 272,808,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedCarryingAmountNet | 337,208,000 cbu_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedCarryingAmountNet |
Accretable discount related to acquired loans [Roll forward] |  |  |
Balance at beginning of year | 997,000 us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield | 1,770,000 us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield |
Accretion recognized | (707,000)us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion | (1,025,000)us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion |
Net reclassification to accretable from nonaccretable | 415,000 us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference | 252,000 us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference |
Balance at end of year | 705,000 us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield | 997,000 us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield |
Consumer Mortgage [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Gross loans, including deferred origination costs | 1,613,384,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 1,582,058,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember |
Allowance for loan losses | (10,286,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | (8,994,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | (7,070,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Consumer Mortgage [Member] | Minimum [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Contract term of loans | 10 years |  |
Consumer Mortgage [Member] | Maximum [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Contract term of loans | 30 years |  |
Business Lending [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Gross loans, including deferred origination costs | 1,262,484,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 1,260,364,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Allowance for loan losses | (15,787,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | (17,507,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | (18,013,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Consumer Indirect [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Gross loans, including deferred origination costs | 833,968,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 740,002,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember |
Allowance for loan losses | (11,544,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | (10,248,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | (9,606,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Consumer Direct [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Gross loans, including deferred origination costs | 184,028,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 180,139,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember |
Allowance for loan losses | (3,083,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | (3,181,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | (3,303,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Home Equity [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Gross loans, including deferred origination costs | 342,342,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 346,520,000 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember |
Allowance for loan losses | $ (2,701,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | $ (1,830,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | $ (1,451,000)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Home Equity [Member] | Maximum [Member] |  |  |
Loans receivable, net [Abstract] |  |  |
Contract term of loans | 30 years |  |

X
- Definition The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities without evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References No definition available. + Details
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- Definition The undiscounted sum of all amounts deemed principal, under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to all loans not accounted for as debt securities that were acquired by completion of a transfer. + References No definition available. + Details
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- Definition The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for as debt securities with evidence of deterioration of credit impairment quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References No definition available. + Details
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- Definition The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References No definition available. + Details
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- Definition Undiscounted amounts deemed principal owed to the acquirer at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit impairment quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References No definition available. + Details
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- Definition The recorded balance, net of any applicable reductions (for example market value adjustments recorded at acquisition). This relates to loans not accounted for as debt securities with no evidence of deterioration of credit quality since origination that were acquired by completion of a transfer. + References No definition available. + Details
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- Definition The undiscounted sum of all amounts deemed principal owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with no evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor expects will be able to collect all contractually required payments receivable. + References No definition available. + Details
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