XML 116 R99.htm IDEA: XBRL DOCUMENT
v3.25.0.1

PENSION PLAN AND OTHER BENEFIT PLANS - Additional Information (Details) - USD ($) |  |  | 12 Months Ended
--- | --- | --- | ---
Jan. 01, 2017 | Oct. 20, 2016 | Dec. 31, 2024 | Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Period of employment multiplier |  |  | 5 years |
Average total life expectancy of participants (years) |  |  | 21 years 8 months 12 days |
Percentage (decrease) increase in unrecognized net loss of the projected benefit obligation |  |  | 0.27 |
Hours requirement to be eligible |  | 1000 hours |  |
All other sources gain (loss) (less than) |  |  | $ 1,000 |
Defined Contribution Profit Sharing, Savings and Investment Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined contribution plan, employer non-discretionary contribution amount | 3.00% |  | 3.00% |
Contribution cost percentage | 50.00% |  | 50.00% |
Defined contribution plan, employer matching contribution, percent of employees' gross pay | 6.00% |  | 6.00% |
Total expense |  |  | $ 1,600,000 | $ 1,400,000
Chemung common stock included in defined contribution plan assets (in shares) |  |  | 112,006 | 124,214
Defined Contribution Supplemental Executive Retirement Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total expense |  |  | $ 700,000 | $ 600,000
Balance in the plan |  |  | 4,000,000.0 | 3,400,000
Pension Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  |  | 29,200,000 | 31,000,000.0
Actuarial loss, increase due to change in discount rate |  |  | $ 1,500,000 |
Percentage of combined loss of expected year end obligations (less than) |  |  | 0.013 |
Other comprehensive income, defined benefit plans, (decrease) increase in net unamortized gain loss arising during period net of tax |  |  | $ (2,000,000) |
Other comprehensive income, defined benefit plans, decrease in net unamortized gain loss arising during period net of tax, due to variance of actual and expected return on plan assets |  |  | $ 900,000 |
Total unrecognized net loss increased percentage of obligation amortization threshold |  |  | 10.00% |
Total unrecognized net loss increased (decreased) percentage of plan assets threshold |  |  | 10.00% |
Increase/(decrease) in the discount rate percentage |  |  | 1.00% |
Increase in net pension cost |  |  | $ 142,000 |
Decrease in net pension cost |  |  | (48,000) |
Decrease in year-end projected benefit obligation |  |  | (2,400,000) |
Increase in year-end projected benefit obligation |  |  | $ 2,800,000 |
Percentage (decrease) increase in unrecognized net loss of the projected benefit obligation |  |  | (0.065) |
Pension Plan | Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Evaluation period of expected long-term return on plan assets |  |  | 3 years |
Pension Plan | Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Evaluation period of expected long-term return on plan assets |  |  | 5 years |
Other Postretirement Benefit Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Other comprehensive income, defined benefit plans, (decrease) increase in net unamortized gain loss arising during period net of tax |  |  | $ 21,000 |
Contribution cost percentage |  |  | 50.00% |
Decrease in accumulated benefit obligation due to change in discount rate |  |  | $ 2,000 |
Increase in accumulated benefit obligation due to discount rate, claims and date experience |  |  | $ 43,000 |
Average future working lifetime of active participants |  |  | 6 years |
Estimated employer contributions in next fiscal year |  |  | $ 15,000 |
Executive Supplemental Pension Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  |  | 900,000 | $ 900,000
Actuarial loss, increase due to change in discount rate |  |  | $ 30,000 |
Total unrecognized net loss increased percentage of obligation amortization threshold |  |  | 10.00% |
Total unrecognized net loss increased (decreased) percentage of plan assets threshold |  |  | 10.00% |
Average total life expectancy of participants (years) |  |  | 9 years 7 months 20 days |
Percentage (decrease) increase in unrecognized net loss of the projected benefit obligation |  |  | (0.011) |
All other sources gain (loss) (less than) |  |  | $ 0 |
Estimated employer contributions in next fiscal year |  |  | 110,000 |
Actuarial gain (loss), increase due to change in mortality losses |  |  | 30,000 |
Defined benefit plan, decrease in total unrecognized net loss |  |  | $ 10,000 |

X
- Definition Refers to the average future working lifetime of active participants. + References No definition available. + Details
Name: | chmg_AverageFutureWorkingLifetimeOfActiveParticipants
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Average Total Life Expectancy of Participants + References No definition available. + Details
Name: | chmg_AverageTotalLifeExpectancyofParticipants
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of contribution cost to be made by retirees, who are going to be continued under the coverage of plan. + References No definition available. + Details
Name: | chmg_ContributionCostPercentage
Namespace Prefix: | chmg_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Benefit Plan, Accumulated Benefit Obligation, Increase (Decrease) + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanAccumulatedBenefitObligationIncreaseDecrease
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Accumulated Benefit Obligation, Increase (Decrease) due to Change in Discount Rate + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanAccumulatedBenefitObligationIncreaseDecreaseDueToChangeInDiscountRate
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Accumulated Benefit Obligation, Increase (Decrease) due to Discount Rate, Claims and Date Experience + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanAccumulatedBenefitObligationIncreaseDecreaseDueToDiscountRateClaimsAndDateExperience
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Decrease In Net Pension Cost + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDecreaseInNetPensionCost
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Increase/(Decrease) In Discount Rate + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostIncreaseDecreaseInDiscountRate
Namespace Prefix: | chmg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Increase In Net Pension Cost + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostIncreaseInNetPensionCost
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss), Increase (Decrease) due to Change in Discount Rate + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanBenefitObligationActuarialGainLossIncreaseDecreaseDueToChangeInDiscountRate
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss), Increase (Decrease) due to Change in Mortality Losses + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanBenefitObligationActuarialGainLossIncreaseDecreaseDueToChangeInMortalityLosses
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss), Percentage of Combined Loss of Expected Year End Obligations + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanBenefitObligationActuarialGainLossPercentageOfCombinedLossOfExpectedYearEndObligations
Namespace Prefix: | chmg_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to the evaluation period for expected long-term return on plan assets for a defined benefit plan. + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanExpectedLongTermReturnOnPlanAssetsEvaluationPeriod
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Benefit Plan, Increase (Decrease) In Total Unrecognized Net Loss + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanIncreaseDecreaseInTotalUnrecognizedNetLoss
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Decrease In Year-end Projected Benefit Obligation + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanPensionPlanWithAccumulatedBenefitObligationInExcessOfPlanAssetsDecreaseInYearEndProjectedBenefitObligation
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Increase In Year-end Projected Benefit Obligation + References No definition available. + Details
Name: | chmg_DefinedBenefitPlanPensionPlanWithAccumulatedBenefitObligationInExcessOfPlanAssetsIncreaseInYearEndProjectedBenefitObligation
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition For a defined contribution plan, the number of sponsoring entity common stock shares included in plan assets. + References No definition available. + Details
Name: | chmg_DefinedContributionPlanAssetsEntityCommonStock
Namespace Prefix: | chmg_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Refers to the balance of a defined contribution plan outstanding as of the balance sheet date. + References No definition available. + Details
Name: | chmg_DefinedContributionPlanBalanceOutstanding
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Defined Contribution Plan, Employer Non-Discretionary Contribution Amount + References No definition available. + Details
Name: | chmg_DefinedContributionPlanEmployerNonDiscretionaryContributionAmount
Namespace Prefix: | chmg_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of annual service hours for employees to be eligible to participate in the defined contribution plan or plans described. + References No definition available. + Details
Name: | chmg_DefinedContributionPlanNumberOfAnnualServiceHoursForEligibility
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase (decrease) in plan's total unrecognized net loss for benefit obligation amortization. + References No definition available. + Details
Name: | chmg_OtherComprehensiveIncomeDefinedBenefitPlansIncreaseDecreaseInNetUnamortizedGainLossArisingDuringPeriodNetOfTax
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other Comprehensive Income, Defined Benefit Plans, Increase (Decrease) in Net Unamortized Gain Loss Arising During Period Net Of Tax, Due to Variance of Actual and Expected Return on Plan Assets + References No definition available. + Details
Name: | chmg_OtherComprehensiveIncomeDefinedBenefitPlansIncreaseDecreaseInNetUnamortizedGainLossArisingDuringPeriodNetOfTaxDueToVarianceOfActualAndExpectedReturnOnPlanAssets
Namespace Prefix: | chmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Pension Plan, Period of Employment Multiplier + References No definition available. + Details
Name: | chmg_PensionPlanPeriodOfEmploymentMultiplier
Namespace Prefix: | chmg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total Unrecognized Net Loss Increase (Decrease) Percentage of Accumulated Benefit Obligation + References No definition available. + Details
Name: | chmg_TotalUnrecognizedNetLossIncreaseDecreasePercentageOfAccumulatedBenefitObligation
Namespace Prefix: | chmg_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total Unrecognized Net Loss Increased(Decreased) Percentage of Plan Assets Threshold + References No definition available. + Details
Name: | chmg_TotalUnrecognizedNetLossIncreasedDecreasedPercentageofPlanAssetsThreshold
Namespace Prefix: | chmg_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase in plan's total unrecognized net loss threshold for benefit obligation amortization. + References No definition available. + Details
Name: | chmg_TotalUnrecognizedNetLossIncreasedPercentageOfObligationAmortizationThreshold
Namespace Prefix: | chmg_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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 Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480794/715-70-50-1 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=chmg_DefinedContributionProfitSharingSavingsAndInvestmentPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=chmg_DefinedContributionSupplementalExecutiveRetirementPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
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: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |