Name:	eqc_CapitalLeaseIncentivesFutureAmortizationExpenseAfterYearFive
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for capital lease incentives during year five of the five succeeding fiscal years.

No definition available.

Name:	eqc_CapitalLeaseIncentivesFutureAmortizationExpenseYearFive
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for capital lease incentives during year four of the five succeeding fiscal years.

No definition available.

Name:	eqc_CapitalLeaseIncentivesFutureAmortizationExpenseYearFour
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for capital lease incentives during year one of the five succeeding fiscal years.

No definition available.

Name:	eqc_CapitalLeaseIncentivesFutureAmortizationExpenseYearOne
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for capital lease incentives during year three of the five succeeding fiscal years.

No definition available.

Name:	eqc_CapitalLeaseIncentivesFutureAmortizationExpenseYearThree
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for capital lease incentives during year two of the five succeeding fiscal years.

No definition available.

Name:	eqc_CapitalLeaseIncentivesFutureAmortizationExpenseYearTwo
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Capital Lease Incentives, Net, Properties Held and Used in Operations

No definition available.

Name:	eqc_CapitalLeaseIncentivesNetPropertiesHeldandUsedinOperations
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Capitalized Lease Incentives, Amortization Expense, Fiscal Year Maturity [Abstract]

No definition available.

Name:	eqc_CapitalizedLeaseIncentivesAmortizationExpenseFiscalYearMaturityAbstract
Namespace Prefix:	eqc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of amortization expense expected to be recognized for deferred charges after year five of the five succeeding fiscal years.

No definition available.

Name:	eqc_DeferredChargesFutureAmortizationExpenseAfterYearFive
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for deferred charges during year five of the five succeeding fiscal years.

No definition available.

Name:	eqc_DeferredChargesFutureAmortizationExpenseYearFive
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for deferred charges during year four of the five succeeding fiscal years.

No definition available.

Name:	eqc_DeferredChargesFutureAmortizationExpenseYearFour
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for deferred charges during year one of the five succeeding fiscal years.

No definition available.

Name:	eqc_DeferredChargesFutureAmortizationExpenseYearOne
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for deferred charges during year three of the five succeeding fiscal years.

No definition available.

Name:	eqc_DeferredChargesFutureAmortizationExpenseYearThree
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of amortization expense expected to be recognized for deferred charges during year two of the five succeeding fiscal years.

No definition available.

Name:	eqc_DeferredChargesFutureAmortizationExpenseYearTwo
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Deferred Costs, Leasing, Amortization Expense, Fiscal Year Maturity [Abstract]

No definition available.

Name:	eqc_DeferredCostsLeasingAmortizationExpenseFiscalYearMaturityAbstract
Namespace Prefix:	eqc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This element is net of accumulated amortization.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
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-URI https://asc.fasb.org/extlink&oid=123394419&loc=d3e40588-112709

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 25
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-URI https://asc.fasb.org/extlink&oid=123408481&loc=SL77919138-209958

Reference 4: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
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