The percentage of ownership interest of common stock or equity participation in a less than wholly owned subsidiary owned by the parent entity.

No definition available.

+ Details

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

- Definition

Represents the total number of common shares of beneficial interest owned by the parent in a less than wholly owned subsidiary.

+ References

No definition available.

+ Details

Name:	eqc_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipSharesOwned
Namespace Prefix:	eqc_
Data Type:	xbrli:sharesItemType
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_MinorityInterestLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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

Noncontrolling Interest in Consolidated Subsidiary - Narrative (Details) (SIR)	0 Months Ended	12 Months Ended
	Mar. 12, 2012	Dec. 31, 2014	Jul. 09, 2014	Jun. 30, 2014	Dec. 31, 2013	Jul. 03, 2013	Jul. 01, 2013	Mar. 31, 2013	Dec. 31, 2012
SIR
Noncontrolling Interest [Line Items]
Less than wholly owned subsidiary, common shares owned (in shares)			22,000,000	22,000,000	22,000,000		22,000,000	22,000,000	22,000,000
Ownership Percentage			0.00%	36.70%	44.20%	44.20%
Less than wholly owned subsidiary, parent ownership interest percentage									56.00%
Ownership percentage prior to initial public offering	100.00%	100.00%