Commitments and Contingencies, Retirement Savings Plan (Details)		12 Months Ended
Jan. 01, 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] \| Subsequent Event [Member]
Defined Contribution Plan [Abstract]
Employer matching contribution up to first 3%	100.00%
Employee contribution threshold for matching percentage	3.00%
Employer matching contribution in excess of first 2%	50.00%
Deferred compensation matched by employer, next match	2.00%
401K [Member] \| Maximum [Member] \| Subsequent Event [Member]
Defined Contribution Plan [Abstract]
Maximum employer matching contribution	4.00%

Defined contribution plan, deferral percentage of employee on their pay on pre-tax basis.

No definition available.

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Namespace Prefix:	erna_
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Period Type:	duration

Percentage of employee contribution to the plan that is fully matched by the employer.

No definition available.

Name:	erna_DefinedContributionPlanEmployeeContributionAtThresholdOne
Namespace Prefix:	erna_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of employee contribution to the plan that is fully matched by the employer.

No definition available.

Name:	erna_DefinedContributionPlanEmployeeContributionAtThresholdTwo
Namespace Prefix:	erna_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage employer matches of the employee's percentage contribution up to a certain percentage matched.

No definition available.

Name:	erna_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchOne
Namespace Prefix:	erna_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage employer matches of the employee's percentage contribution in excess of certain percentage matched.

No definition available.

Name:	erna_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchTwo
Namespace Prefix:	erna_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	us-gaap_DefinedContributionPlanAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: