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v3.23.1

Commitments and Contingencies, Royalty Agreements (Details) |  | 1 Months Ended
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Mar. 22, 2021 | Nov. 30, 2018
Investor Royalty Agreement [Member] |  |
Royalty Agreements [Abstract] |  |
Percentage of royalty receive equal to revenues from sale of business | 4.00% |
Percentage of payment of additional royalty on gross sales |  | 1.00%
Collaborator Royalty Agreement [Member] |  |
Royalty Agreements [Abstract] |  |
Percentage of royalty payable |  | 6.00%

X
- Definition Percentage of royalty payable from one party to another in licensing agreement. + References No definition available. + Details
Name: | erna_LossContingencyPercentageOfRoyaltyPayable
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of additional royalty payable on gross sales by the entity. + References No definition available. + Details
Name: | erna_PercentageOfPaymentOfAdditionalRoyaltyOnGrossSales
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of royalty payable equal to revenues generated from disposition of business. + References No definition available. + Details
Name: | erna_PercentageOfRoyaltyPayableEqualToRevenuesFromSaleOfBusiness
Namespace Prefix: | erna_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_TypeOfArrangementAxis=erna_InvestorRoyaltyAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TypeOfArrangementAxis=erna_CollaboratorRoyaltyAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |