Percentage of common stock shares outstanding considered for equity number of shares under equity incentive plan.

No definition available.

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- Definition

Number of shares issuable under share-based payment arrangement.

+ References

No definition available.

+ Details

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Namespace Prefix:	erna_
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Period Type:	duration

- References

No definition available.

+ Details

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

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Period Type:	instant

- Definition

Number of additional shares authorized for issuance under share-based payment arrangement.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

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Data Type:	xbrli:durationItemType
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Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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- Details

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- Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Stock-Based Compensation, Equity Incentive Plans (Details) - shares			12 Months Ended
	Jan. 01, 2024	Jan. 01, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Stock Options [Member]
Stock-based Compensation [Abstract]
Stock option outstanding (in shares)			389,000	359,000	199,000
2020 Equity Incentive Plan [Member]
Stock-based Compensation [Abstract]
Percentage of number of shares of common stock outstanding			5.00%
Number of shares issuable (in shares)		256,000
Number of common stock shares to be issued (in shares)			684,000
Stock option outstanding (in shares)			296,000
Restricted stock units, granted (in shares)			0
2020 Equity Incentive Plan [Member] \| Subsequent Event [Member]
Stock-based Compensation [Abstract]
Number of shares issuable (in shares)	271,000
2020 Equity Incentive Plan [Member] \| Stock Options [Member]
Stock-based Compensation [Abstract]
Stock-based compensation shares authorized (in shares)			724,000
Increase in stock-based compensation shares authorized (in shares)			300,000
2020 Equity Incentive Plan [Member] \| Incentive Stock Options [Member] \| Maximum [Member]
Stock-based Compensation [Abstract]
Stock based compensation stock option term period			10 years
2020 Equity Incentive Plan [Member] \| Nonqualified Stock Options [Member] \| Maximum [Member]
Stock-based Compensation [Abstract]
Stock based compensation stock option term period			10 years
2021 Inducement Plan [Member]
Stock-based Compensation [Abstract]
Number of common stock shares to be issued (in shares)			68,000
Stock option outstanding (in shares)				4,000
Restricted stock units, outstanding (in shares)				1,000
2021 Inducement Plan [Member] \| Maximum [Member]
Stock-based Compensation [Abstract]
Stock-based compensation shares authorized (in shares)			75,000