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=66902209&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_PropertyNumberElevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFourteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Real Estate Properties - Summary of Properties Sold (Details) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) ft² building property	Jan. 31, 2017 USD ($) ft² building property	Mar. 31, 2017 USD ($) ft² building property	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) ft² building
Real Estate Properties [Line Items]
Gain (Loss) on Sale			$ 16,454	$ 36,666
Disposed of by Sale
Real Estate Properties [Line Items]
Number of Properties \| property			3
Number of Buildings \| building			3		62
Square Footage (in sqft) \| ft²			827,204		8,000,000
Gross Sales Price			$ 113,125		$ 1,300,000
Gain (Loss) on Sale			$ 16,454
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 \| 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