XML 17 R48.htm IDEA: XBRL DOCUMENT
v2.4.1.9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) | 12 Months Ended | 1 Months Ended |
--- | --- | --- | ---
Dec. 31, 2014 Segment | Mar. 31, 2008 Branch | Nov. 30, 2013 Branch | Dec. 31, 2013
LOANS [Abstract] |  |  |  |
Period of delinquency after which a loan is placed on non-accrual status | 90 days |  |  |
Number of consecutive months for which loans remain current before non-accrual loans are returned to accrual status | 6 months |  |  |
Rolling historical period of net losses used in evaluating general component of valuation allowance for loans not impaired but classified as substandard and special mention | 5 years |  |  |
Number of most recent years of actual loss history used in determining historical loss experience for all other unclassified loans | 2 years |  |  |
WEALTH MANAGEMENT GROUP FEE INCOME [Abstract] |  |  |  |
Unaudited market value of trust assets under administration | $ 1,956,000,000 us-gaap_AssetsUnderManagementCarryingAmount |  |  | $ 1,888,000,000 us-gaap_AssetsUnderManagementCarryingAmount
Segment Reporting [Abstract] |  |  |  |
Number of operating segments | 2 us-gaap_NumberOfOperatingSegments |  |  |
M&T Bank Branch Offices [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Number of branches acquired |  | 3 chmg_NumberOfBranchesAcquired / us-gaap_BusinessAcquisitionAxis = chmg_MTBankBranchOfficesMember |  |
Intangible assets acquired | 21,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_BusinessAcquisitionAxis = chmg_MTBankBranchOfficesMember |  |  |
Partners Trust Bank [Member] | Trust Business [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Intangible assets acquired | 2,400,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_BusinessAcquisitionAxis = chmg_PartnersTrustBankMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = chmg_TrustBusinessMember |  |  |
Expected useful life | 15 years |  |  |
Canton Bancorp, Inc. [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Intangible assets acquired | 8,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_BusinessAcquisitionAxis = chmg_CantonBancorpIncMember |  |  |
Fort Orange Financial Corp [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Intangible assets acquired | 1,100,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_BusinessAcquisitionAxis = chmg_FortOrangeFinancialCorpMember |  |  |
Expected useful life | 10 years |  |  |
Bank of America Branch Offices [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Number of branches acquired |  |  | 6 chmg_NumberOfBranchesAcquired / us-gaap_BusinessAcquisitionAxis = chmg_BankOfAmericaMember |
Intangible assets acquired | 1,600,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_BusinessAcquisitionAxis = chmg_BankOfAmericaMember |  |  |
Bank of America Branch Offices [Member] | Core Deposit Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Expected useful life | 7 years |  |  |
MT Branch Offices and Canton Bancorp, Inc. Member] [Member] | Core Deposit Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Expected useful life | 7 years 3 months |  |  |
MT Branch Offices and Canton Bancorp, Inc. Member] [Member] | Customer Relationship Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Expected useful life | 7 years 3 months |  |  |
Non-qualified Deferred Compensation Plan [Member] |  |  |  |
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items] |  |  |  |
Maximum annual installments period | 10 years |  |  |
Directors' Compensation Plan [Member] | Director [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of shares authorized per calendar year (in shares) | 20,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = chmg_DirectorsCompensationPlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |  |
Required service period | 12 months |  |  |
Trading days period | 30 days |  |  |
Incentive Compensation Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of shares authorized per calendar year (in shares) | 10,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = chmg_IncentiveCompensationPlanMember |  |  |
Cash compensation | $ 300,000 chmg_CashCompensation / us-gaap_PlanNameAxis = chmg_IncentiveCompensationPlanMember |  |  |
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of shares authorized per calendar year (in shares) | 15,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember |  |  |
Age limit for forfeiture of stock award | 65 years |  |  |
Restricted Stock [Member] | Awards Vesting Each Year Commencing with First Anniversary Date of Award [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Award vesting percentage (in hundredths) | 20.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_VestingAxis = chmg_ShareBasedCompensationAwardVestingEachYearCommencingWithFirstAnniversaryDateOfAwardMember |  |  |
Restricted Stock [Member] | Awards Vesting on Fifth Anniversary Date [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Award vesting percentage (in hundredths) | 100.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_VestingAxis = chmg_ShareBasedCompensationAwardVestingOnFifthAnniversaryDateMember |  |  |
Defined Contribution Profit Sharing, Savings and Investment Plan [Member] |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |
Number of annual service hours required for eligibility (in hours) | 1000 hours |  |  |
Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Normal retirement benefit as percentage of final average compensation (in hundredths) | 1.20%chmg_NormalRetirementBenefit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Number of consecutive years considered in final average compensation | 5 years |  |  |
Number of prior years considered in final average compensation | 10 years |  |  |
Maximum service period | 25 years |  |  |
Normal retirement additional benefit (in hundredths) | 1.00%chmg_NormalRetirementAdditionalBenefit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Maximum additional service years | 10 years |  |  |
Percentage of average monthly compensation in excess of covered compensation for each year of credited service (in hundredths) | 0.65%chmg_PercentageOfAverageMonthlyCompensationInExcessOfCoveredCompensationForEachYearOfCreditedService / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |  |
Maximum period of credited service | 35 years |  |  |
Covered compensation period | 35 years |  |  |
Defined Benefit Health Care Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Minimum eligible age | 55 years |  |  |
Contribution percentage (in hundredths) | 40.00%chmg_ContributionPercentageBeforeAmendment / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Retiree premium percentage (in hundredths) | 100.00%chmg_RetireePremiumPercentage / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Cost of coverage contribution (in hundredths) | 50.00%chmg_CostOfCoverageContribution / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Contribution percentage after amendment (in hundredths) | 50.00%chmg_PremiumContributionPercentageAfterAmendment / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Contribution cost percentage (in hundredths) | 50.00%chmg_ContributionCostPercentage / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |
Minimum [Member] | Defined Benefit Health Care Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Retiree age group range | 55 years |  |  |
Maximum [Member] | Defined Benefit Health Care Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Retiree age group range | 65 years |  |  |
Buildings [Member] | Minimum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives | 15 years |  |  |
Buildings [Member] | Maximum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives | 50 years |  |  |
Equipment and Furniture [Member] | Minimum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives | 3 years |  |  |
Equipment and Furniture [Member] | Maximum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives | 10 years |  |  |

X
- Definition Age limit applicable to forfeiture of stock, the stock is to be forfeited if the participant retires early. + References No definition available. + Details
Name: | chmg_AgeLimitForForfeitureOfStockAward
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Cash compensation which is paid under incentive compensation plan. + References No definition available. + Details
Name: | chmg_CashCompensation
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of contribution cost to be made by retirees, who are going to be continued under the coverage of plan. + References No definition available. + Details
Name: | chmg_ContributionCostPercentage
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of contribution made under self-insure health care plan, before amendment. + References No definition available. + Details
Name: | chmg_ContributionPercentageBeforeAmendment
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of contribution made under self-insure health care plan. + References No definition available. + Details
Name: | chmg_CostOfCoverageContribution
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The period for covered compensation, which is average of social security taxable wage bases in effect. + References No definition available. + Details
Name: | chmg_CoveredCompensationPeriod
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of annual service hours for employees to be eligible to participate in the defined contribution plan or plans described. + References No definition available. + Details
Name: | chmg_DefinedContributionPlanNumberOfAnnualServiceHoursForEligibility
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | chmg_LOANSAbstract
Namespace Prefix: | chmg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to maximum additional period considered in final average compensation, during which additional 1% of average monthly compensation for each additional year of service is added. + References No definition available. + Details
Name: | chmg_MaximumAdditionalServiceYears
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum annual installments period which can be opted by plan participants under Nonqualified Deferred Compensation Plan. + References No definition available. + Details
Name: | chmg_MaximumAnnualInstallmentsPeriod
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum period of credited service considered to apply excess of covered compensation for each year of credited service. + References No definition available. + Details
Name: | chmg_MaximumPeriodOfCreditedService
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to maximum period considered in final average compensation. + References No definition available. + Details
Name: | chmg_MaximumServicePeriod
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Minimum age for eligibility for coverage under self-insure health care plan, before amendment. + References No definition available. + Details
Name: | chmg_MinimumAgeForEligibilityBeforeAmendment
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of normal retirement benefit in terms of average monthly compensation resulting for each additional year. + References No definition available. + Details
Name: | chmg_NormalRetirementAdditionalBenefit
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of normal retirement benefit in terms of final average compensation resulting from maximum period of 25 years. + References No definition available. + Details
Name: | chmg_NormalRetirementBenefit
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the number of branches acquired during the period. + References No definition available. + Details
Name: | chmg_NumberOfBranchesAcquired
Namespace Prefix: | chmg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the number of consecutive months for which loans remain current before non-accrual loans are returned to accrual status. + References No definition available. + Details
Name: | chmg_NumberOfConsecutiveMonthsForWhichLoansRemainCurrentBeforeNonAccrualLoansAreReturnedToAccrualStatus
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers consecutive period considered in final average compensation. + References No definition available. + Details
Name: | chmg_NumberOfConsecutiveYearsConsideredInFinalAverageCompensation
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the number of most recent years of actual loss history used in determining historical loss experience for all other unclassified loans. + References No definition available. + Details
Name: | chmg_NumberOfMostRecentYearsOfActualLossHistoryUsedInDeterminingHistoricalLossExperienceForAllOtherUnclassifiedLoans
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to prior period considered in consecutive period of final average compensation. + References No definition available. + Details
Name: | chmg_NumberOfPriorYearsConsideredInFinalAverageCompensation
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the percentage of average monthly compensation in excess of covered compensation for each year of credited service. + References No definition available. + Details
Name: | chmg_PercentageOfAverageMonthlyCompensationInExcessOfCoveredCompensationForEachYearOfCreditedService
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the period of delinquency after which a loan is placed on non-accrual status. + References No definition available. + Details
Name: | chmg_PeriodOfDelinquencyAfterWhichALoanIsPlacedOnNonAccrualStatus
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of premium contribution made under self-insure health care plan. + References No definition available. + Details
Name: | chmg_PremiumContributionPercentageAfterAmendment
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Eligible age of current and future retirees to be continued under coverage of plan. + References No definition available. + Details
Name: | chmg_RetireeAgeGroupRange
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of premium to be paid by retiree under self-insure health care plan. + References No definition available. + Details
Name: | chmg_RetireePremiumPercentage
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the rolling historical period of net losses used in evaluating general component of valuation allowance for loans not impaired but classified as substandard and special mention. + References No definition available. + Details
Name: | chmg_RollingHistoricalPeriodOfNetLossesUsedInEvaluatingGeneralComponentOfValuationAllowanceForLoansNotImpairedButClassifiedAsSubstandardAndSpecialMention
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of trading days considered in valuing common stock . + References No definition available. + Details
Name: | chmg_TradingDaysPeriod
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | chmg_WealthManagementGroupFeeIncomeAbstract
Namespace Prefix: | chmg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The carrying amount of assets an investment adviser manages on behalf of investors. + References No definition available. + Details
Name: | us-gaap_AssetsUnderManagementCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
Name: | us-gaap_NumberOfOperatingSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SegmentReportingDisclosureOfOtherInformationAboutEntitysReportableSegmentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of vesting of share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=chmg_BankOfAmericaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=chmg_CantonBancorpIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=chmg_FortOrangeFinancialCorpMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=chmg_MTBankBranchOfficesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=chmg_MTBranchOfficesAndCantonBancorpIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=chmg_PartnersTrustBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationShareBasedPaymentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedContributionPlanNameAxis=chmg_DefinedContributionProfitSharingSavingsAndInvestmentPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=chmg_DirectorsCompensationPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=chmg_IncentiveCompensationPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_OfficeEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |