XML 55 R45.htm IDEA: XBRL DOCUMENT v3.22.2.2

LOANS AND ALLOWANCE FOR LOAN LOSSES - Troubled Debt Restructuring Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) contract loan	Sep. 30, 2021 USD ($) loan contract	Sep. 30, 2022 USD ($) contract loan	Sep. 30, 2021 USD ($) contract loan	Dec. 31, 2021 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, troubled debt restructuring	$ 5,900,000		$ 5,900,000		$ 10,300,000
Financing receivable, troubled debt restructuring, purchased with credit deterioration, increase	300,000		300,000		1,900,000
Financing receivable, modifications, recorded investment, still accruing	1,400,000		1,400,000		5,600,000
Financing receivable, modifications, recorded investment, nonaccrual status	4,400,000		4,400,000		4,700,000
Additional amounts committed to customers with loans classified as troubled debt restructurings	0		0		$ 0
Number of Loans | loan		2		6
Increase in allowance for loan losses related to troubled debt restructurings		$ 200,000		$ 1,900,000
Charge offs	$ 277,000	$ 234,000	$ 1,306,000	$ 650,000
Number of days past due after which a loan is considered to be in payment default			90 days
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | contract	0	0	0	0
Commercial Mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Charge offs	$ 0	$ 44,000	$ 687,000	$ 44,000
Commercial Mortgages | Commercial mortgages, other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	2	0	6
Charge offs		$ 0		$ 0

X

- Definition

Represents additional amounts committed to customers with outstanding loans that are classified as troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	chmg_AdditionalAmountsCommittedToCustomersWithLoansClassifiedAsTroubledDebtRestructurings
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings and are on nonaccrual status as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	chmg_FinancingReceivableModificationsRecordedInvestmentNonaccrualStatus
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings and have been still accruing interest under the modified terms.

+ References

No definition available.

+ Details

Name:	chmg_FinancingReceivableModificationsRecordedInvestmentStillAccruing
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Financing Receivable, Troubled Debt Restructuring, Purchased with Credit Deterioration, Increase

+ References

No definition available.

+ Details

Name:	chmg_FinancingReceivableTroubledDebtRestructuringPurchasedwithCreditDeteriorationIncrease
Namespace Prefix:	chmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Number Of Days Past Due After Which A Loan Is Considered To Be In Payment Default

+ References

No definition available.

+ Details

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

X

- Definition

Amount of increase (decrease) in allowance for credit loss on financing receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of writeoff of financing receivable, charged against allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

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

X

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

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

X

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Details

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

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=chmg_CommercialMortgagesOtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: