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Commitments and Contingencies, Legal Matters (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Legal Matters [Abstract] |  |
Aggregate settlement amount payable |  | $ 0.5
Litigation settlement, amount | $ 0.5 | $ 1.2

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

X
- Definition Amount payable to other party in judgment or settlement of litigation. + References No definition available. + Details
Name: | erna_LitigationSettlementAmountPayable
Namespace Prefix: | erna_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount awarded to other party in judgment or settlement of litigation. + References No definition available. + Details
Name: | us-gaap_LitigationSettlementAmountAwardedToOtherParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration