XML 81 R65.htm IDEA: XBRL DOCUMENT
v3.21.1

LOANS AND ALLOWANCE FOR LOAN LOSSES - Troubled Debt Restructuring (Details) | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) loan borrower instrument | Dec. 31, 2019 USD ($) loan | Dec. 31, 2018 USD ($) loan
Trouble debt restructurings [Abstract] |  |  |
Recorded investment in troubled debt restructurings | $ | $ 6,700,000 | $ 9,000,000.0 | $ 6,800,000
Specific reserves allocated to troubled debt restructuring | $ | 400,000 | 2,300,000 | 900,000
Troubled debt restructurings accruing interest under modified terms | $ | 2,800,000 | 900,000 | 800,000
Troubled debt restructurings on non-accrual status | $ | 3,900,000 | 8,100,000 | 6,000,000.0
Additional amounts committed to customers with loans classified as troubled debt restructurings | $ | $ 17,000 | $ 0 | $ 0
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 15 | 3 | 2
Pre-Modification Outstanding Recorded Investment | $ | $ 5,100,000 | $ 4,483,000 | $ 491,000
Post-Modification Outstanding Recorded Investment | $ | 5,100,000 | 4,483,000 | 491,000
Increase in allowance for loan losses related to troubled debt restructurings | $ | 200,000 | 1,700,000 | 400,000
Troubled debt restructurings, charge offs | $ | $ 0 | $ 0 | $ 0
Number of days past due after which a loan is considered to be in payment default | 90 days |  |
Financing receivable, modifications, subsequent default, number of loans | instrument | 1 |  |
Financing receivable, modifications, subsequent default, recorded investment | $ | $ 170,000 |  |
Commercial mortgages | Commercial mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 4 | 1 |
Pre-Modification Outstanding Recorded Investment | $ | $ 1,297,000 | $ 4,223,000 |
Post-Modification Outstanding Recorded Investment | $ | $ 1,297,000 | $ 4,223,000 |
Residential Mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 4 | 1 |
Pre-Modification Outstanding Recorded Investment | $ | $ 997,000 | $ 123,000 |
Post-Modification Outstanding Recorded Investment | $ | $ 997,000 | $ 123,000 |
Consumer Loans | Home equity lines and loans |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 3 | 1 |
Pre-Modification Outstanding Recorded Investment | $ | $ 738,000 | $ 137,000 |
Post-Modification Outstanding Recorded Investment | $ | $ 738,000 | $ 137,000 |
Financing receivable, modifications, subsequent default, number of loans | instrument | 1 |  |
Financing receivable, modifications, subsequent default, recorded investment | $ | $ 170,000 |  |
Commercial And Consumer Portfolio Segment |  |  |
Trouble debt restructurings [Abstract] |  |  |
Financing receivable, modifications, loan balance remaining in modified status, modified more than once | $ | $ 20,100,000 |  |
Financing receivable, number of loans remaining in modified status | 31 |  |
Financing receivable, modifications, loan balance remaining in modified status | $ | $ 20,800,000 |  |
Financing receivable, number of loans remaining in modified status, modified more than once | 18 |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 1,064 |  |
Post-Modification Outstanding Recorded Investment | $ | $ 211,200,000 |  |
Principal Forgiveness | Commercial mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  | 1 |
Principal Forgiveness | Residential Mortgage |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 1 |  |
Interest Rate Below Market Reduction | Consumer Loans | Home equity lines and loans |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  | 1 |
Payment Deferral |  |  |
Trouble debt restructurings [Abstract] |  |  |
Financing receivable, modifications, number of days past due | 30 days |  |
Payment Deferral | Commercial mortgages |  |  |
Trouble debt restructurings [Abstract] |  |  |
Financing receivable, modifications, number of borrowers | borrower | 3 |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 4 |  |
Payment Deferral | Commercial mortgages | Substandard | Non-accrual Status |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 3 |  |
Payment Deferral | Commercial mortgages | Substandard | Non-accrual Status | 30 - 59 Days Past Due |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 2 |  |
Payment Deferral | Home equity lines and loans |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 3 |  |
Payment Deferral | Home equity lines and loans | Substandard | Non-accrual Status |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 3 |  |
Payment Deferral | Residential Mortgage |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 3 |  |
Payment Deferral | Residential Mortgage | Non-accrual Status |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 3 |  |
Payment Deferral | Residential Mortgage | Substandard | Non-accrual Status |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 2 |  |
Payment Deferral | Residential Mortgage | Substandard | Non-accrual Status | 30 - 59 Days Past Due |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 1 |  |
Extended Maturity and Interest Rate Below Market Reduction | Residential Mortgage |  |  |
Trouble debt restructurings [Abstract] |  |  |
Troubled debt restructuring, extension of maturity date, duration |  | 13 years |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  | 1 |
Extended Maturity and Interest Rate Below Market Reduction | Consumer Loans | Home equity lines and loans |  |  |
Trouble debt restructurings [Abstract] |  |  |
Troubled debt restructuring, extension of maturity date, duration |  | 3 years |
Commercial and industrial | Commercial, and Agricultural |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 4 |  | 2
Pre-Modification Outstanding Recorded Investment | $ | $ 2,068,000 |  | $ 491,000
Post-Modification Outstanding Recorded Investment | $ | $ 2,068,000 |  | $ 491,000
Commercial and industrial | Interest Rate Below Market Reduction |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 2 |  |
Commercial and industrial | Interest Rate Below Market Reduction | Non-accrual Status |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 1 |  |
Commercial and industrial | Extended Maturity |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 2 |  |
Commercial and industrial | Extended Maturity and Interest Rate Below Market Reduction |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 1 |  |
Commercial and industrial | Extended Maturity and Interest Rate Below Market Reduction | Commercial, and Agricultural |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  |  | 2

X
- Definition Represents additional amounts committed to customers with outstanding loans that are classified as troubled debt restructurings. + References No definition available. + Details
Name: | chmg_AdditionalAmountsCommittedToCustomersWithLoansClassifiedAsTroubledDebtRestructurings
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Financing Receivable, Modifications, Extension Period + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsExtensionPeriod
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivable, Modifications, Loan Balance Remaining in Modified Status + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsLoanBalanceRemainingInModifiedStatus
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Financing Receivable, Modifications, Loan Balance Remaining in Modified Status, Modified More than Once + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsLoanBalanceRemainingInModifiedStatusModifiedMoreThanOnce
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Financing Receivable, Modifications, Number of Borrowers + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsNumberOfBorrowers
Namespace Prefix: | chmg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Financing Receivable, Modifications, Number of Days Past Due + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsNumberOfDaysPastDue
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings and are on nonaccrual status as of the balance sheet date. + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsRecordedInvestmentNonaccrualStatus
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings and have been still accruing interest under the modified terms. + References No definition available. + Details
Name: | chmg_FinancingReceivableModificationsRecordedInvestmentStillAccruing
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Financing Receivable, Number of Loans Remaining in Modified Status + References No definition available. + Details
Name: | chmg_FinancingReceivableNumberOfLoansRemainingInModifiedStatus
Namespace Prefix: | chmg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Financing Receivable, Number of Loans Remaining in Modified Status, Modified More than Once + References No definition available. + Details
Name: | chmg_FinancingReceivableNumberOfLoansRemainingInModifiedStatusModifiedMoreThanOnce
Namespace Prefix: | chmg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Financing Receivable, Troubled Debt Restructuring, Purchased with Credit Deterioration, Increase + References No definition available. + Details
Name: | chmg_FinancingReceivableTroubledDebtRestructuringPurchasedwithCreditDeteriorationIncrease
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | chmg_LoansByClassModifiedAsTroubledDebtRestructuringsAbstract
Namespace Prefix: | chmg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the number of days past due after which a loan is considered to be in payment default. + References No definition available. + Details
Name: | chmg_NumberOfDaysPastDueAfterWhichALoanIsConsideredToBeInPaymentDefault
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | chmg_TroubleDebtRestructuringsAbstract
Namespace Prefix: | chmg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase (decrease) of allowance reserve for credit loss. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of financing receivables that have been modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after troubled debt restructuring, of modified financing receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, before troubled debt restructuring, of financing receivable to be modified. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of financing receivable modified as troubled debt restructuring. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554 + Details
Name: | us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 34 -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 34 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524 + Details
Name: | us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Reflects the amount of the write-down related to a troubled debt restructuring. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554 + Details
Name: | us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=chmg_CommercialMortgagesOtherLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=chmg_CommercialAndConsumerPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_PrincipalForgivenessMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_InterestRateBelowMarketReductionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentPerformanceStatusAxis=chmg_NonAccrualStatusMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivables30To59DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=chmg_ExtendedMaturityAndInterestRateBelowMarketReductionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_EquitySecuritiesByIndustryAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=chmg_CommercialAndAgriculturalPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=chmg_NonAccrualStatusMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |