XML 116 R99.htm IDEA: XBRL DOCUMENT
v3.24.0.1

PENSION PLAN AND OTHER BENEFIT PLANS - Target Allocations Of Plan Assets (Details) - Pension Plan | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
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) | 41.00% | 39.00%
Expected return on assets | 11.80% |
Mid-cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (in hundredths) | 2.00% | 2.00%
Expected return on assets | 11.50% |
Small-cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (in hundredths) | 1.00% | 1.00%
Expected return on assets | 9.70% |
International equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (in hundredths) | 3.00% | 3.00%
Expected return on assets | 6.90% |
Intermediate fixed income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (in hundredths) | 37.00% | 43.00%
Expected return on assets | 7.00% |
Alternative assets |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (in hundredths) | 0.00% | 0.00%
Expected return on assets | 2.90% |
Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (in hundredths) | 16.00% | 12.00%
Expected return on assets | 1.20% |
Minimum | Large cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 30.00% |
Minimum | Mid-cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 0.00% |
Minimum | Small-cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 0.00% |
Minimum | International equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 0.00% |
Minimum | Intermediate fixed income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 33.00% |
Minimum | Alternative assets |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 0.00% |
Minimum | Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 0.00% |
Maximum | Large cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 60.00% |
Maximum | Mid-cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 8.00% |
Maximum | Small-cap domestic equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 6.00% |
Maximum | International equities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 8.00% |
Maximum | Intermediate fixed income |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 63.00% |
Maximum | Alternative assets |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 15.00% |
Maximum | Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation, minimum (in hundredths) | 20.00% |

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=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: |