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Commitments and Contingencies, Royalty Agreements (Details)		1 Months Ended
	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

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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: