XML 59 R47.htm IDEA: XBRL DOCUMENT
v3.8.0.1

FAIR VALUE - Quantitative Information (Details) - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Impaired Loans: | Non-recurring |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | $ 350 | $ 507
Other real estate owned: | Non-recurring |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | 1,832 | 1,940
Other real estate owned: | Non-recurring | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | 283 | 382
Derivative Liabilities | Recurring | Historical trend |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Liabilities, fair value disclosure | $ 50 | $ 75
Derivative Liabilities | Recurring | Historical trend | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Credit default rate | 5.52% | 5.67%
Derivative Liabilities | Recurring | Historical trend | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Credit default rate | 5.52% | 5.67%
Derivative Liabilities | Recurring | Historical trend | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Credit default rate | 5.52% | 5.67%
Commercial and Industrial | Impaired Loans: | Non-recurring | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | $ 12 | $ 96
Commercial and Industrial | Impaired Loans: | Non-recurring | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 0.00% | 0.00%
Commercial and Industrial | Impaired Loans: | Non-recurring | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 0.00% | 36.07%
Commercial and Industrial | Impaired Loans: | Non-recurring | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 0.00% | 33.02%
Commercial and Industrial | Other real estate owned: | Non-recurring | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value |  | $ 1,483
Commercial and Industrial | Other real estate owned: | Non-recurring | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 10.00% | 10.00%
Commercial and Industrial | Other real estate owned: | Non-recurring | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 22.95% | 22.95%
Commercial and Industrial | Other real estate owned: | Non-recurring | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 19.75% | 19.75%
Commercial mortgages, other | Impaired Loans: | Non-recurring | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | $ 338 | $ 411
Commercial mortgages, other | Impaired Loans: | Non-recurring | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 21.98% | 10.00%
Commercial mortgages, other | Impaired Loans: | Non-recurring | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 69.81% | 89.98%
Commercial mortgages, other | Impaired Loans: | Non-recurring | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 55.51% | 51.35%
Commercial mortgages, other | Other real estate owned: | Non-recurring |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | $ 1,474 |
Home equity lines and loans | Other real estate owned: | Non-recurring | Sales comparison |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Fair value | $ 75 | $ 75
Residential mortgages | Other real estate owned: | Non-recurring | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 17.28% | 17.28%
Residential mortgages | Other real estate owned: | Non-recurring | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 39.78% | 27.97%
Residential mortgages | Other real estate owned: | Non-recurring | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 20.39% | 20.77%
Home equity lines and loans | Other real estate owned: | Non-recurring | Sales comparison | Minimum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 20.80% | 20.80%
Home equity lines and loans | Other real estate owned: | Non-recurring | Sales comparison | Maximum |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 20.80% | 20.80%
Home equity lines and loans | Other real estate owned: | Non-recurring | Sales comparison | Weighted Average |  |
Information related to Level 3 non-recurring fair value measurement [Abstract] |  |
Discount to appraised value | 20.80% | 20.80%

X
- Definition Fair Value Inputs, Credit Default Rate + References No definition available. + Details
Name: | chmg_FairValueInputsCreditDefaultRate
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair Value Inputs, Discount To Appraised Value + References No definition available. + Details
Name: | chmg_FairValueInputsDiscountToAppraisedValue
Namespace Prefix: | chmg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | chmg_InformationRelatedToLevel3NonRecurringFairValueMeasurementAbstract
Namespace Prefix: | chmg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
Name: | us-gaap_AssetsFairValueDisclosureNonrecurring
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregation of the liabilities reported on the balance sheet measured at fair value on a recurring basis by the entity. + References No definition available. + Details
Name: | us-gaap_LiabilitiesFairValueDisclosureRecurring
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=chmg_ImpairedLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=chmg_OtherRealEstateOwnedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=chmg_SalesComparisonMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=chmg_HistoricalTrendMember
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: |

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_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

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

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