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Leases, Sublease Agreement (Details) $ in Thousands		12 Months Ended
	Apr. 18, 2019 ft²	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Leases [Abstract]
Currently rented area | ft²	999
Percentage of annual rent increase	2.25%
Future Lease Payments, Sublease Agreement [Abstract]
2023		$ 84
2024		86
2025		88
2026		75
Total		333
Sublease payments received		$ 100	$ 100

X

- Definition

The subleases rentable area for properties currently rented.

+ References

No definition available.

+ Details

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Namespace Prefix:	erna_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of increase in annual lease payment for subleases for each year.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of minimum sublease rentals to be received by the seller-lessee for sale-leaseback transactions accounted for using the deposit method or as a financing.

+ References

No definition available.

+ Details

Name:	erna_SaleLeasebackTransactionsFutureMinimumSubleaseRentals
Namespace Prefix:	erna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

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Namespace Prefix:	erna_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of minimum sublease rentals for sale-leaseback transactions accounted for using the deposit method or as a financing to be received by the seller-lessee in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	erna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of minimum sublease rentals for sale-leaseback transactions accounted for using the deposit method or as a financing to be received by the seller-lessee in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	erna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of minimum sublease rentals for sale-leaseback transactions accounted for using the deposit method or as a financing to be received by the seller-lessee in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

Name:	erna_SaleLeasebackTransactionsFutureMinimumSubleaseRentalsWithinThreeYears
Namespace Prefix:	erna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of minimum sublease rentals for sale-leaseback transactions accounted for using the deposit method or as a financing to be received by the seller-lessee in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	erna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_LeasesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of cash inflow from lease payment, classified as operating activity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 45
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=123420820&loc=SL77919320-209978

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 45
-Paragraph 7
-URI https://asc.fasb.org/extlink&oid=123420820&loc=SL77919327-209978

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration