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Commitments and Contingencies, Retirement Savings Plan (Details) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2023 | Dec. 31, 2023 | Dec. 31, 2022
Maximum [Member] |  |  |
Defined Contribution Plan [Abstract] |  |  |
Employees contribution, deferral percentage of their pay on a pre-tax basis |  |  | 90.00%
401K [Member] |  |  |
Defined Contribution Plan [Abstract] |  |  |
Employees contribution, deferral percentage of their pay on a pre-tax basis | 100.00% |  |
Employer matching contribution up to first 3% | 3.00% |  |
Employee contribution threshold for matching percentage | 50.00% |  |
Employer matching contribution in excess of first 2% | 2.00% |  |
Deferred compensation matched by employer, next match | 4.00% |  |
401K [Member] | Maximum [Member] |  |  |
Defined Contribution Plan [Abstract] |  |  |
Employer matching contributions |  | $ 0.1 |

X
- Definition Defined contribution plan, deferral percentage of employee on their pay on pre-tax basis. + References No definition available. + Details
Name: | erna_DefinedContributionPlanDeferralPercentOfTheirPayOnPreTaxBasis
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of employee contribution to the plan that is fully matched by the employer. + References No definition available. + Details
Name: | erna_DefinedContributionPlanEmployeeContributionAtThresholdOne
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of employee contribution to the plan that is fully matched by the employer. + References No definition available. + Details
Name: | erna_DefinedContributionPlanEmployeeContributionAtThresholdTwo
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage employer matches of the employee's percentage contribution up to a certain percentage matched. + References No definition available. + Details
Name: | erna_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchOne
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage employer matches of the employee's percentage contribution in excess of certain percentage matched. + References No definition available. + Details
Name: | erna_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchTwo
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=erna_RetirementPlan401KMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |