XML 60 R41.htm IDEA: XBRL DOCUMENT v2.4.1.9
FAIR VALUE (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Financial Assets [Abstract]    
Total available for sale securities $ 266,307us-gaap_AvailableForSaleSecurities $ 280,507us-gaap_AvailableForSaleSecurities
Trading assets 601us-gaap_TradingSecurities 549us-gaap_TradingSecurities
Other real estate owned [Member]    
Consumer loans [Abstract]    
Total other real estate owned, net   3,100us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Financial Assets [Abstract]    
Total available for sale securities 31,321us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
31,219us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Significant Other Observable Inputs (Level 2) [Member]    
Financial Assets [Abstract]    
Total available for sale securities 234,986us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
249,288us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Significant Unobservable Inputs (Level 3) [Member]    
Financial Assets [Abstract]    
Total available for sale securities 0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Recurring [Member]    
Financial Assets [Abstract]    
Obligations of U.S. Government and U.S. Government sponsored enterprises 170,447chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
181,673chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Mortgage-backed securities, residential 59,182us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
61,660us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Collateralized mortgage obligations 231chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
338chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Obligations of states and political subdivisions 31,152chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
31,451chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate bonds and notes 1,528chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,533chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
SBA loan pools 1,260chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,304chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trust Preferred securities 2,024chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2,028chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate stocks 483chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
520chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total available for sale securities 266,307us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
280,507us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trading assets 601us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
549us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Financial Assets [Abstract]    
Obligations of U.S. Government and U.S. Government sponsored enterprises 31,266chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
31,115chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Mortgage-backed securities, residential 0us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Collateralized mortgage obligations 0chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Obligations of states and political subdivisions 0chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate bonds and notes 0chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
SBA loan pools 0chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trust Preferred securities 0chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate stocks 55chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
104chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total available for sale securities 31,321us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
31,219us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trading assets 601us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
549us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Financial Assets [Abstract]    
Obligations of U.S. Government and U.S. Government sponsored enterprises 139,181chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
150,558chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Mortgage-backed securities, residential 59,182us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
61,660us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Collateralized mortgage obligations 231chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
338chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Obligations of states and political subdivisions 31,152chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
31,451chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate bonds and notes 1,528chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,533chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
SBA loan pools 1,260chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,304chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trust Preferred securities 2,024chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2,028chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate stocks 428chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
416chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total available for sale securities 234,986us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
249,288us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trading assets 0us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]    
Financial Assets [Abstract]    
Obligations of U.S. Government and U.S. Government sponsored enterprises 0chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Mortgage-backed securities, residential 0us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Collateralized mortgage obligations 0chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Obligations of states and political subdivisions 0chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate bonds and notes 0chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
SBA loan pools 0chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trust Preferred securities 0chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate stocks 0chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total available for sale securities 0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trading assets 0us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
0us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Non-recurring [Member] | Impaired Loans [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 2,993chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,593chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Consumer loans [Abstract]    
Home equity lines and loans   52chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans 2,993us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,645us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Other real estate owned [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 2,496chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,063chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Residential mortgages 10chmg_CommercialMortgageLoansResidentialMortgagesFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
 
Consumer loans [Abstract]    
Home equity lines and loans   2chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total other real estate owned, net 2,506us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,065us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Impaired Loans [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Consumer loans [Abstract]    
Home equity lines and loans   0chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other real estate owned [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Residential mortgages 0chmg_CommercialMortgageLoansResidentialMortgagesFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
 
Consumer loans [Abstract]    
Home equity lines and loans   0chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total other real estate owned, net 0us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Impaired Loans [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Consumer loans [Abstract]    
Home equity lines and loans   0chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other real estate owned [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Residential mortgages 0chmg_CommercialMortgageLoansResidentialMortgagesFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
 
Consumer loans [Abstract]    
Home equity lines and loans   0chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total other real estate owned, net 0us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Impaired Loans [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 2,993chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,593chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Consumer loans [Abstract]    
Home equity lines and loans   52chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans 2,993us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,645us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other real estate owned [Member]    
Impaired Loans, Fair Value Disclosure [Abstract]    
Commercial mortgages 2,496chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
3,063chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Residential mortgages 10chmg_CommercialMortgageLoansResidentialMortgagesFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
 
Consumer loans [Abstract]    
Home equity lines and loans   2chmg_HomeEquityLinesLoans
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total other real estate owned, net $ 2,506us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
$ 3,065us-gaap_OtherRealEstateAndForeclosedAssets
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember