Name:	eqc_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipSharesOwned
Namespace Prefix:	eqc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Represents the number of common shares of beneficial interest of equity method investee sold by an investor.

No definition available.

Name:	eqc_EquityMethodInvestmentNumberOfSharesSold
Namespace Prefix:	eqc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

This element represents the amount of coverage for property insurance pursuant to an insurance program arranged by the equity method investee.

No definition available.

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

Represents the number of other companies which are shareholders of related party of the entity.

No definition available.

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

Represents the number of parking spaces.

No definition available.

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

Represents the service agreements entered into by the entity for availing services from other entities.

No definition available.

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

Represents the number of managing trustees with related parties.

No definition available.

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

Represents the amount of reimbursement payable to related party if specified minimum common share price maintain during the one year period after the date on which the reimbursement is approved by shareholders.

No definition available.

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

Represents the amount of reimbursement payable to related party if specified minimum common share price maintain during the one year period between the first and second anniversaries of the date on which the reimbursement is approved by shareholders.

No definition available.

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

Related Party Reimbursement Amount Paid

No definition available.

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

Expenses recognized during the period resulting from business and property management transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

No definition available.

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

Expenses recognized during the period resulting from business management transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

No definition available.

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

Expenses recognized during the period resulting from property management and construction supervision agreement (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

No definition available.

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

Represents the amount of lease payment made under the lease agreement entered into with the related party by the entity.

No definition available.

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

Related Party Transaction Lease Payment, Initial Term

No definition available.

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

Represents the information pertaining to lease term of office space, which the entity leases to related parties.

No definition available.

Name:	eqc_RelatedPartyTransactionLeaseTerm
Namespace Prefix:	eqc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Amount of legal fees and costs incurred for combined directors' and officers' liability insurance policy.

No definition available.

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

Represents the term of the license agreement entered into with the related party by the entity.

No definition available.

Name:	eqc_RelatedPartyTransactionLicenseAgreementTerm
Namespace Prefix:	eqc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the license fees to be paid to related parties.

No definition available.

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

Related Party Transaction, Management Fee, Monthly Expense

No definition available.

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

Represents the number of renewal options of lease arrangement entered into with the related party by the entity.

No definition available.

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

Represents the percentage of base business management fees payable in common shares.

No definition available.

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

Represents the renewal term of lease arrangement entered into with the related party by the entity.

No definition available.

Name:	eqc_RelatedPartyTransactionRenewalTermOfLeaseArrangement
Namespace Prefix:	eqc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Share Price, During First and Second Year After Date

No definition available.

Name:	eqc_SharePriceDuringFirstandSecondYearAfterDate
Namespace Prefix:	eqc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

Share Price, During One Year Period After Date

No definition available.

Name:	eqc_SharePriceDuringOneYearPeriodAfterDate
Namespace Prefix:	eqc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

Carrying amount as of the balance sheet date of obligations due all related parties.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(k)(1))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(3),(4))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.17)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_EquityMethodInvestmentAggregateCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This item represents the amount of net sales proceeds received on disposal of an equity method investment.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 35

-Paragraph 35

-URI http://asc.fasb.org/extlink&oid=49116238&loc=d3e32847-111569

Name:	us-gaap_EquityMethodInvestmentNetSalesProceeds
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

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

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

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

Percentage of subsidiary's or equity investee's stock owned by parent company before stock transaction.

No definition available.

Name:	us-gaap_SaleOfStockPercentageOfOwnershipBeforeTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Price of a single share of a number of saleable stocks of a company.

No definition available.

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

Number of shares issued in lieu of cash for services contributed to the entity. Number of shares includes, but is not limited to, shares issued for services contributed by vendors and founders.

No definition available.

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

Name:	dei_LegalEntityAxis=eqc_SelectIncomeREITMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_TransactionTypeAxis=eqc_AmendedAndRestateBusinessManagementAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

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

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

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