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=98514028&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
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberThreeMember
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFourMember
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Data Type:	na
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFifteenMember
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Data Type:	na
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberSixteenMember
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Data Type:	na
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberSeventeenMember
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberElevenMember
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberThirteenMember
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- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFourteenMember
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Real Estate Properties - Summary of Properties Sold (Details) $ in Thousands	1 Months Ended				3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2017 USD ($) ft² property building	Apr. 30, 2017 USD ($) ft² property building	Mar. 31, 2017 USD ($) ft² property building	Jan. 31, 2017 USD ($) ft² property building	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) ft² property building	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) ft² building
Real Estate Properties [Line Items]
Gain (Loss) on Sale					$ 3,136	$ 106,375	$ 19,590	$ 143,041
Disposed of by Sale
Real Estate Properties [Line Items]
Number of Properties \| property							6
Number of Buildings \| building							9		62
Square Footage (in sqft) \| ft²							1,698,310		8,000,000
Gross Sales Price							$ 211,625		$ 1,300,000
Gain (Loss) on Sale							$ 19,590
Disposed of by Sale \| 111 Market Place
Real Estate Properties [Line Items]
Number of Properties \| property				1
Number of Buildings \| building				1
Square Footage (in sqft) \| ft²				589,380
Gross Sales Price				$ 60,100
Gain (Loss) on Sale				$ (5,968)
Disposed of by Sale \| Cabot Business Park Land
Real Estate Properties [Line Items]
Number of Properties \| property			0
Number of Buildings \| building			0
Square Footage (in sqft) \| ft²			0
Gross Sales Price			$ 575
Gain (Loss) on Sale			$ (57)
Disposed of by Sale \| Parkshore Plaza
Real Estate Properties [Line Items]
Number of Properties \| property		1
Number of Buildings \| building		4
Square Footage (in sqft) \| ft²		271,072
Gross Sales Price		$ 40,000
Gain (Loss) on Sale		$ (2,460)
Disposed of by Sale \| 25 S. Charles Street
Real Estate Properties [Line Items]
Number of Properties \| property		1
Number of Buildings \| building		1
Square Footage (in sqft) \| ft²		359,254
Gross Sales Price		$ 24,500
Gain (Loss) on Sale		$ (3,483)
Disposed of by Sale \| 802 Delaware Avenue
Real Estate Properties [Line Items]
Number of Properties \| property	1
Number of Buildings \| building	1
Square Footage (in sqft) \| ft²	240,780
Gross Sales Price	$ 34,000
Gain (Loss) on Sale	$ 9,079
Disposed of by Sale \| 4515 Seton Center Parkway
Real Estate Properties [Line Items]
Number of Properties \| property			1
Number of Buildings \| building			1
Square Footage (in sqft) \| ft²			117,265
Disposed of by Sale \| 4516 Seton Center Parkway
Real Estate Properties [Line Items]
Number of Properties \| property			1
Number of Buildings \| building			1
Square Footage (in sqft) \| ft²			120,559
Disposed of by Sale \| Seton Center
Real Estate Properties [Line Items]
Number of Properties \| property			2
Number of Buildings \| building			2
Square Footage (in sqft) \| ft²			237,824
Gross Sales Price			$ 52,450
Gain (Loss) on Sale			$ 22,479