Name:	eqc_DiscontinuedOperationGainsLossesOnEarlyExtinguishmentOfDebtNetOfTax
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Number Of Buildings Held For Sale

No definition available.

Name:	eqc_NumberOfBuildingsHeldForSale
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

This element represents the number of buildings held for use by the entity.

No definition available.

Name:	eqc_NumberOfBuildingsHeldForUse
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

This element represents the number of buildings sold or agreed to be sold by the entity.

No definition available.

Name:	eqc_NumberOfBuildingsSold
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

This element represents the number of properties sold or agreed to be sold by the entity.

No definition available.

Name:	eqc_NumberOfPropertiesSold
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of properties held for sale during the period.

No definition available.

Name:	eqc_NumberOfRealEstatePropertiesHeldForSale
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The number of long-lived held and used properties held for use.

No definition available.

Name:	eqc_NumberOfRealEstatePropertiesHeldForUse
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the reversal of amount of write-down of assets recognized in the income statement. Includes, but is not limited to, reversal of losses from tangible assets, intangible assets and goodwill.

No definition available.

Name:	eqc_ReversalOfLossOnAssetImpairment
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Area of a real estate property.

No definition available.

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

Amount after tax of (gain) loss recognized for the (reversal of write-down) write-down to fair value, less cost to sell, of a discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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

Cash received for the sale of real estate that is not part of an investing activity during the current period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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

Amount of increase in real estate investments related to improvements for entities with a substantial portion of business acquiring and holding investment real estate.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Subparagraph (SX 210.5-04.(c) Schedule III)

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

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.

No definition available.

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

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=eqc_CentralBusinessDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=eqc_SuburbanPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=eqc_CentralBusinessDistrictAndSuburbanPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: