XML 58 R46.htm IDEA: XBRL DOCUMENT v3.21.1

FAIR VALUE - Quantitative Information (Details) - Significant Unobservable Inputs (Level 3) - Other real estate owned: - Non-recurring - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Information related to Level 3 non-recurring fair value measurement [Abstract]
Assets, fair value disclosure	$ 115	$ 237
Residential mortgages | Sales comparison
Information related to Level 3 non-recurring fair value measurement [Abstract]
Assets, fair value disclosure	$ 115	$ 126
Residential mortgages | Sales comparison | Minimum
Information related to Level 3 non-recurring fair value measurement [Abstract]
Discount to appraised value	20.80%	20.80%
Residential mortgages | Sales comparison | Maximum
Information related to Level 3 non-recurring fair value measurement [Abstract]
Discount to appraised value	20.80%	20.80%
Residential mortgages | Sales comparison | Weighted Average
Information related to Level 3 non-recurring fair value measurement [Abstract]
Discount to appraised value	20.80%	20.80%
Commercial mortgages, other | Sales comparison
Information related to Level 3 non-recurring fair value measurement [Abstract]
Assets, fair value disclosure		$ 111
Commercial mortgages, other | Sales comparison | Minimum
Information related to Level 3 non-recurring fair value measurement [Abstract]
Discount to appraised value		20.80%
Commercial mortgages, other | Sales comparison | Maximum
Information related to Level 3 non-recurring fair value measurement [Abstract]
Discount to appraised value		20.80%
Commercial mortgages, other | Sales comparison | Weighted Average
Information related to Level 3 non-recurring fair value measurement [Abstract]
Discount to appraised value		20.80%

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

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
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_ValuationTechniqueAxis=chmg_SalesComparisonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
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: