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v3.20.1

SUBSEQUENT EVENT (Details) - USD ($) | Apr. 23, 2020 | Feb. 04, 2020
--- | --- | ---
Subsequent Event [Line Items] |  |
Participating credit facility receivable, ownership interest, amount |  | $ 4,200,000
Participating credit facility receivable, amount |  | $ 36,000,000
Subsequent Event |  |
Subsequent Event [Line Items] |  |
Proceeds from participation agreement | $ 461,309 |
Participating credit facility receivable, ownership interest, amount | 4,200,000 |
Participating credit facility receivable, amount | $ 36,000,000 |

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- Definition Participating Credit Facility Receivable, Amount + References No definition available. + Details
Name: | chmg_ParticipatingCreditFacilityReceivableAmount
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Participating Credit Facility Receivable, Ownership Interest, Amount + References No definition available. + Details
Name: | chmg_ParticipatingCreditFacilityReceivableOwnershipInterestAmount
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Proceeds From Participation Agreement + References No definition available. + Details
Name: | chmg_ProceedsFromParticipationAgreement
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |