The charge incurred against earnings during the period to reduce the carrying amount of properties sold to fair value.

No definition available.

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

- Definition

Represents the number of buildings impaired.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of assets impaired.

+ References

No definition available.

+ Details

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

- Definition

Represents the minimum percentage of probability for realization of largest amount of benefits associated with tax position.

+ References

No definition available.

+ Details

Name:	eqc_DeferredTaxAssetsMinimumPercentageOfProbabilityOfRealizationOfLargestAmountOfTaxBenefit
Namespace Prefix:	eqc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Disposal Group, Including Discontinued Operation, Gain (Loss) on Sales of Assets and Asset Impairment Charges

+ References

No definition available.

+ Details

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

- Definition

Represents environmental remediation costs accrued at the balance sheet date.

+ References

No definition available.

+ Details

Name:	eqc_EnvironmentalRemediationCostsAccrued
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The charge against earnings in the period to reduce the carrying amount of real estate properties to fair value of continuing operations.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of ownership held in the subsidiary either directly or indirectly.

+ References

No definition available.

+ Details

Name:	eqc_OwnershipPercentageHeldInSubsidiary
Namespace Prefix:	eqc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Cumulative translation adjustment resulting from translating foreign currency financial statements into the reporting currency. Reported in equity as part of accumulated other comprehensive income.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 30

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6915805&loc=d3e32022-110900

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 30

-Section 45

-Paragraph 20

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6915805&loc=d3e32211-110900

+ Details

Name:	us-gaap_TranslationAdjustmentFunctionalToReportingCurrencyNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=eqc_PersonalPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingAndBuildingImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
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Period Type:

Summary of Significant Accounting Policies - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013 property	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Percentage of investments in subsidiaries	100.00%eqc_OwnershipPercentageHeldInSubsidiary
Loss on asset impairment	$ 185,067,000	$ 124,253,000	$ 0
Loss on asset impairment in discontinuing operations		79,800,000
Number of properties impaired		39eqc_AssetsImpairedPropertiesNumber
Number of buildings impaired		93eqc_AssetsImpairedBuildingsNumber
Losses on asset impairment for properties sold		23,100,000
Accrued environmental remediation costs	500,000	400,000
Minimum percentage of likelihood of realization of tax benefits	50.00%
Foreign currency translation adjustments	$ (48,900,000)	$ (26,600,000)
Maximum
Property, Plant and Equipment [Line Items]
Maximum percentage of investment accounted for under equity method of accounting	50.00%
Buildings and improvements \| Maximum
Property, Plant and Equipment [Line Items]
Maximum estimated useful life	40 years
Personal property \| Maximum
Property, Plant and Equipment [Line Items]
Maximum estimated useful life	12 years