Represents the period, for which commitments are generally made to make commercial draw notes.

No definition available.

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- Definition

Represents the period, for which commitments are generally made to make real estate and home equity loans.

+ References

No definition available.

+ Details

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Namespace Prefix:	chmg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Refer to interest rate on fixed-rate commitments to make commercial draw notes.

+ References

No definition available.

+ Details

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Namespace Prefix:	chmg_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Refer to interest rate on the fixed-rate commitments to make loans.

+ References

No definition available.

+ Details

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Namespace Prefix:	chmg_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Refers to maturity period of the fixed-rate commitments to make loans.

+ References

No definition available.

+ Details

Name:	chmg_MaturityPeriodOfFixedRateCommitmentsToMakeLoans
Namespace Prefix:	chmg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnfundedLoanCommitmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	chmg_InterestRateTypeAxis=chmg_FixedInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
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COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Allowance for credit losses	$ 20,471	$ 22,517	$ 20,075	$ 19,659
Unfunded Loan Commitment
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Allowance for credit losses	$ 743	$ 919	$ 1,048	$ 0
Minimum \| Fixed Rate
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Interest rate on fixed-rate commitments to make loans	5.63%
Maturity period of fixed-rate commitments to make loans (years)	4 years
Commitments period to make fixed-rate commercial draw notes (months)	3 months
Interest rate on fixed-rate commitments to make commercial draw notes (in hundredths)	2.79%
Maximum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitments period to make real estate and home equity loans (days)	60 days
Maximum \| Fixed Rate
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Interest rate on fixed-rate commitments to make loans	7.38%
Maturity period of fixed-rate commitments to make loans (years)	30 years
Commitments period to make fixed-rate commercial draw notes (months)	24 months
Interest rate on fixed-rate commitments to make commercial draw notes (in hundredths)	8.17%