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/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

+ Details

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

- Definition

Amount before tax of income (loss) from an individually significant component disposed of or held-for-sale including the portion attributable to the noncontrolling interest. Excludes discontinued operations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=SL51724579-110230

+ Details

Name:	us-gaap_IncomeLossFromIndividuallySignificantComponentDisposedOfOrHeldForSaleExcludingDiscontinuedOperationsBeforeIncomeTax
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
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberThreeMember
Namespace Prefix:
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberFourMember
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Data Type:	na
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_PropertyNumberNineteenMember
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_A1601DryCreekDriveMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_A777EastEisenhowerParkwayMember
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_A8750BrynMawrAvenueMember
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Real Estate Properties - Summary of Properties Sold (Details) $ in Thousands	1 Months Ended					3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) ft² building property	Aug. 31, 2018 USD ($) ft² building property	May 31, 2018 USD ($) ft² building property	Mar. 31, 2018 USD ($) ft² building property	Feb. 28, 2018 USD ($) ft² building property	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) ft² building property	Sep. 30, 2017 USD ($)
Real Estate Properties [Line Items]
Gain on Sale						$ 20,877	$ 25,080	$ 253,025	$ 44,670
Disposed of by Sale
Real Estate Properties [Line Items]
Number of Properties \| property								6
Number of Buildings \| building								8
Square Footage (in sqft) \| ft²								4,115,411
Gross Sales Price								$ 1,024,186
Gain on Sale								253,060
Net income included in continued operations						$ 100	$ 2,400	$ 110,400	$ 7,400
Disposed of by Sale \| 1600 Market Street
Real Estate Properties [Line Items]
Number of Properties \| property					1
Number of Buildings \| building					1
Square Footage (in sqft) \| ft²					825,968
Gross Sales Price					$ 160,000
Gain on Sale					$ 54,599
Disposed of by Sale \| 600 West Chicago Avenue
Real Estate Properties [Line Items]
Number of Properties \| property					1
Number of Buildings \| building					2
Square Footage (in sqft) \| ft²					1,561,477
Gross Sales Price					$ 510,000
Gain on Sale					$ 107,790
Disposed of by Sale \| 5073, 5075, & 5085 S. Syracuse Street
Real Estate Properties [Line Items]
Number of Properties \| property				1
Number of Buildings \| building				1
Square Footage (in sqft) \| ft²				248,493
Gross Sales Price				$ 115,186
Gain on Sale				$ 42,762
Disposed of by Sale \| 1601 Dry Creek Drive
Real Estate Properties [Line Items]
Number of Properties \| property			1
Number of Buildings \| building			1
Square Footage (in sqft) \| ft²			552,865
Gross Sales Price			$ 68,500
Gain on Sale			$ 26,979
Disposed of by Sale \| 777 East Eisenhower Parkway
Real Estate Properties [Line Items]
Number of Properties \| property		1
Number of Buildings \| building		1
Square Footage (in sqft) \| ft²		290,530
Gross Sales Price		$ 29,500
Gain on Sale		$ 5,321
Disposed of by Sale \| 8750 Bryn Mawr Avenue
Real Estate Properties [Line Items]
Number of Properties \| property	1
Number of Buildings \| building	2
Square Footage (in sqft) \| ft²	636,078
Gross Sales Price	$ 141,000
Gain on Sale	$ 15,609