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

Disposal Group, Not Discontinued Operation, Percentage Of Equity Interests In Fee Simple Owner Sold

+ References

No definition available.

+ Details

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

- Definition

Gain (Loss) on Sale of Properties, Release Of Escrow Deposits

+ References

No definition available.

+ Details

Name:	eqc_GainLossOnSaleOfPropertiesReleaseOfEscrowDeposits
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Escrow deposits related to property sales in noncash investing and financing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

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-Section 50
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-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586

+ Details

Name:	us-gaap_EscrowDepositsRelatedToPropertySales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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
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-Publisher FASB
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-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
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-SubTopic 10
-Section 50
-Paragraph 3A
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=SL51724579-110230

+ Details

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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:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_A109BrooklineAvenueMember
Namespace Prefix:
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Balance Type:
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_A333108thAvenueNEMember
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_GeorgetownGreenAndHarrisBuildingsMember
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- Details

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Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_ResearchParkMember
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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, 2020 USD ($) ft² property building	Mar. 31, 2020 USD ($) ft² property building	Feb. 29, 2020 USD ($) ft² building property	Jun. 30, 2019 USD ($) ft² property building	Apr. 30, 2019 USD ($) ft² building property	Mar. 31, 2019 USD ($) ft² building property	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) ft² building property	Jun. 30, 2019 USD ($) ft² property building	Dec. 31, 2019 USD ($)
Real Estate Properties [Line Items]
Gain on Sale							$ 26,916	$ 227,166	$ 446,536	$ 420,203
Disposed of by Sale
Real Estate Properties [Line Items]
Number of Properties \| property									3	3
Number of Buildings \| building									4	6
Square Footage (in sqft) \| ft²									961,437	2,651,453
Gross Sale Price									$ 756,500	$ 812,100
Gain on Sale									444,530	420,152
Disposed of by Sale \| 109 Brookline Avenue
Real Estate Properties [Line Items]
Number of Properties \| property			1
Number of Buildings \| building			1
Square Footage (in sqft) \| ft²			285,556
Gross Sale Price			$ 270,000
Gain on Sale			$ 225,190
Disposed of by Sale \| 333 108th Avenue NE
Real Estate Properties [Line Items]
Number of Properties \| property		1
Number of Buildings \| building		1
Square Footage (in sqft) \| ft²		435,406
Gross Sale Price		$ 401,500
Gain on Sale		$ 194,424							194,400
Net income included in continued operations							$ 28	3,700	$ 193,200	7,300
Disposed of by Sale \| Georgetown-Green and Harris Buildings
Real Estate Properties [Line Items]
Number of Properties \| property	1
Number of Buildings \| building	2
Square Footage (in sqft) \| ft²	240,475
Gross Sale Price	$ 85,000
Gain on Sale	$ 24,916
Disposed of by Sale \| 1735 Market Street
Real Estate Properties [Line Items]
Number of Properties \| property						1
Number of Buildings \| building						1
Square Footage (in sqft) \| ft²						1,286,936
Gross Sale Price						$ 451,600
Gain on Sale						$ 192,985				193,000
Net income included in continued operations								$ 100		$ 197,200
Percentage of equity interests in fee simple owner sold							100.00%		100.00%
Disposed of by Sale \| 600 108th Avenue NE
Real Estate Properties [Line Items]
Number of Properties \| property					1
Number of Buildings \| building					1
Square Footage (in sqft) \| ft²					254,510
Gross Sale Price					$ 195,000
Gain on Sale					$ 149,009
Disposed of by Sale \| Research Park
Real Estate Properties [Line Items]
Number of Properties \| property				1
Number of Buildings \| building				4
Square Footage (in sqft) \| ft²				1,110,007
Gross Sale Price				$ 165,500
Gain on Sale				$ 78,158
Consideration held in escrow											$ 2,000
Additional gain on sale of properties, release of escrow deposits							$ 2,000		$ 2,000