XML 122 R105.htm IDEA: XBRL DOCUMENT v3.25.0.1

PENSION PLAN AND OTHER BENEFIT PLANS - Target Allocations Of Plan Assets (Details) - Pension Plan	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	100.00%	100.00%
Expected return on assets	5.50%	5.50%
Large cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	15.00%	41.00%
Expected return on assets	12.10%
Mid-cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	0.00%	2.00%
Expected return on assets	0.00%
Small-cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	0.00%	1.00%
Expected return on assets	0.00%
International equities
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	0.00%	3.00%
Expected return on assets	0.00%
Emerging market equities
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	0.00%	0.00%
Expected return on assets	0.00%
Intermediate fixed income
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	69.00%	37.00%
Expected return on assets	2.70%
Alternative assets
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	0.00%	0.00%
Expected return on assets	0.00%
Cash
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets (in hundredths)	16.00%	16.00%
Expected return on assets	1.40%
Minimum | Large cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Mid-cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Small-cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | International equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Emerging market equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Intermediate fixed income
Defined Benefit Plan Disclosure [Line Items]
Target allocation	60.00%
Minimum | Alternative assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Minimum | Cash
Defined Benefit Plan Disclosure [Line Items]
Target allocation	0.00%
Maximum | Large cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	30.00%
Maximum | Mid-cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	6.00%
Maximum | Small-cap domestic equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	5.00%
Maximum | International equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	6.00%
Maximum | Emerging market equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	5.00%
Maximum | Intermediate fixed income
Defined Benefit Plan Disclosure [Line Items]
Target allocation	100.00%
Maximum | Alternative assets
Defined Benefit Plan Disclosure [Line Items]
Target allocation	15.00%
Maximum | Cash
Defined Benefit Plan Disclosure [Line Items]
Target allocation	25.00%

X

- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanEquitySecuritiesUsLargeCapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanEquitySecuritiesUsMidCapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanEquitySecuritiesUsSmallCapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanEquitySecuritiesNonUsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=chmg_DefinedBenefitPlanEquitySecuritiesEmergingMarketEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=chmg_AlternativeAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanCashMember
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: