Area of Real Estate Property Disposed

No definition available.

Name:	eqc_AreaofRealEstatePropertyDisposed
Namespace Prefix:	eqc_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Number Of Real Estate Properties Sold

+ References

No definition available.

+ Details

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

- Definition

The element represents the aggregate sales price excluding mortgage debt repayments and closing costs, of real estate properties sold or agreed to be sold by the entity.

+ References

No definition available.

+ Details

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

- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Details

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

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Summary of Properties Sold (Details) $ in Thousands	1 Months Ended			3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) ft² building property	Feb. 29, 2016 USD ($) ft² building property	Jan. 31, 2013 building property	Mar. 31, 2016 USD ($) ft² building property	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) ft² building
Real Estate Properties [Line Items]
Number of Properties \| property			3
Number of Buildings \| building			18
Gain on Sale				$ 36,666	$ 5,868
Disposed of by Sale
Real Estate Properties [Line Items]
Number of Properties \| property				3
Number of Buildings \| building				11		135
Square Footage (in sqft) \| ft²				856,831		18,900,000
Gross Sales Price				$ 122,615		$ 2,000,000
Gain on Sale				$ 36,666
Disposed of by Sale \| Executive Park
Real Estate Properties [Line Items]
Number of Properties \| property		1
Number of Buildings \| building		9
Square Footage (in sqft) \| ft²		427,443
Gross Sales Price		$ 50,865
Gain on Sale		$ 16,532
Disposed of by Sale \| 3330 N Washington Boulevard
Real Estate Properties [Line Items]
Number of Properties \| property	1
Number of Buildings \| building	1
Square Footage (in sqft) \| ft²	55,719
Gross Sales Price	$ 11,250
Gain on Sale	$ 5,457
Disposed of by Sale \| 111 East Kilbourn Avenue
Real Estate Properties [Line Items]
Number of Properties \| property	1
Number of Buildings \| building	1
Square Footage (in sqft) \| ft²	373,669
Gross Sales Price	$ 60,500
Gain on Sale	$ 14,677