XML 26 R73.htm IDEA: XBRL DOCUMENT v2.4.1.9
FAIR VALUES (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Financial Assets [Abstract]    
Total available for sale securities $ 280,507us-gaap_AvailableForSaleSecurities $ 346,016us-gaap_AvailableForSaleSecurities
Trading assets 549us-gaap_TradingSecurities 366us-gaap_TradingSecurities
Recurring [Member]    
Financial Assets [Abstract]    
Obligations of U.S. Government and U.S. Government sponsored enterprises 181,673chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
188,106chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Mortgage-backed securities, residential 61,660us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
104,356us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Collateralized mortgage obligations 338chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,015chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Obligations of states and political subdivisions 31,451chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
38,376chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate bonds and notes 1,533chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2,946chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
SBA loan pools 1,304chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,488chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trust Preferred securities 2,028chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2,034chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate stocks 520chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
7,695chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total available for sale securities 280,507us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
346,016us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trading assets 549us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
366us-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 31,115chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
31,262chmg_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 104chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
7,279chmg_CorporateStocksFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total available for sale securities 31,219us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
38,541us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trading assets 549us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
366us-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 150,558chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
156,844chmg_ObligationsOfUSGovernmentAndUSGovernmentSponsoredEnterprisesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Mortgage-backed securities, residential 61,660us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
104,356us-gaap_MortgageBackedSecuritiesAvailableForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Collateralized mortgage obligations 338chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,015chmg_CollateralizedMortgageObligationsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Obligations of states and political subdivisions 31,451chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
38,376chmg_ObligationsOfStatesAndPoliticalSubdivisionsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate bonds and notes 1,533chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2,946chmg_CorporateBondsAndNotesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
SBA loan pools 1,304chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
1,488chmg_SmallBusinessAdministrationPoolLoansFairValuedisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Trust Preferred securities 2,028chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
2,034chmg_TrustPreferredSecuritiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Corporate stocks 416chmg_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 249,288us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
307,475us-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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   460chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 3,593chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
485chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Consumer loans [Abstract]    
Home equity lines and loans 52chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
54chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 3,645us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
999us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Non-recurring [Member] | Other Real Estate Owned [Member]    
Commercial and agricultural [Abstract]    
Commercial and industrial   101chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 3,063chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
266chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Residential mortgages   106chmg_CommercialMortgageLoansResidentialMortgagesFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Consumer loans [Abstract]    
Home equity lines and loans 2chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
65chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 3,065us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
538us-gaap_LoansReceivableFairValueDisclosure
/ 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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   0chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 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_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   0chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 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_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0us-gaap_LoansReceivableFairValueDisclosure
/ 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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   0chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 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_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   0chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 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_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
0us-gaap_LoansReceivableFairValueDisclosure
/ 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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   460chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 2,905chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
485chmg_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_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
54chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net 2,957us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_ImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
999us-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]    
Commercial and agricultural [Abstract]    
Commercial and industrial   101chmg_CommercialAndIndustrialLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Commercial mortgages [Abstract]    
Commercial mortgages other 3,063chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
266chmg_CommercialMortgageLoansOtherFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Residential mortgages   106chmg_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_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
65chmg_HomeEquityLinesAndLoansFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Total impaired loans/ other real estate owned, net $ 3,065us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
$ 538us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByAssetClassAxis
= chmg_OtherRealEstateOwnedMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember