Commitments (Details) - AstraZeneca $ in Millions	1 Months Ended
Apr. 30, 2018 USD ($)
Commitments and Contingencies
Subscription agreement one-time milestone payment on net sales	$ 5.0
Term of the milestone payment on net sales	3 months
Subscription agreement one-time milestone payment on first commercial sale	$ 10.0
Term of the milestone payment on first commercial sale	2 years

Represents the amount for subscription agreement one-time milestone payment on commercial sales.

No definition available.

Name:	ettx_SubscriptionAgreementOneTimeMilestonePaymentOnCommercialSales
Namespace Prefix:	ettx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount for subscription agreement one-time milestone payment on net sales.

+ References

No definition available.

+ Details

Name:	ettx_SubscriptionAgreementOneTimeMilestonePaymentOnNetSales
Namespace Prefix:	ettx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the term of the milestone payment for achieving the first commercial sale in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	ettx_TermOfMilestonePaymentForCommercialSale
Namespace Prefix:	ettx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the term of the milestone payment for achieving a specified cumulative net sales in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	ettx_TermOfMilestonePaymentForNetSales
Namespace Prefix:	ettx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=ettx_AstraZenecaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: