Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldOtherAdjustments
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents other adjustments on certain loans acquired in transfer not accounted for as debt securities cash flows expected to be collected.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodCashFlowsExpectedToBeCollectedOtherAdjustments
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents other adjustments on certain loans acquired in transfer not accounted for as debt securities contractually required payments receivable.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAcquiredDuringPeriodContractuallyRequiredPaymentsReceivableOtherAdjustments
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents income accretion on certain loans acquired in transfer not accounted for as debt securities cash flows expected to be collected.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCashFlowsExpectedToBeCollectedIncomeAccretion
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents income accretion on certain loans acquired in transfer not accounted for as debt securities cash flows not expected to be collected.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCashFlowsNotExpectedToBeCollectedIncomeAccretion
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents other adjustments on certain loans acquired in transfer not accounted for as debt securities cash flows not expected to be collected.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCashFlowsNotExpectedToBeCollectedOtherAdjustments
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents income accretion on certain loans acquired in transfer not accounted for as debt securities contractually required payments receivable at fair value.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesContractuallyRequiredPaymentsReceivableAtFairValueIncomeAccretion
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents other adjustments on certain loans acquired in transfer not accounted for as debt securities contractually required payments receivable at fair value.

No definition available.

Name:	chmg_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesContractuallyRequiredPaymentsReceivableAtFairValueOtherAdjustments
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents income accretion on certain loans acquired in transfer not accounted for as debt securities contractually required payments receivable.

No definition available.