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

No definition available.

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

- 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

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate dividends paid during the period for each share of preferred stock outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_PreferredStockDividendsPerShareCashPaid
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate dividends declared during the period for each share of preferred stock outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_PreferredStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
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_StatementClassOfStockAxis=us-gaap_SeriesDPreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=eqc_MarketStreetPhiladelphiaPA1735Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Events - Narrative (Details) $ / shares in Units, $ in Thousands												12 Months Ended
	Feb. 15, 2019 $ / shares	Jan. 29, 2019 USD ($) ft²	Jan. 11, 2019 $ / shares	Nov. 15, 2018 $ / shares	Oct. 29, 2018 $ / shares	Aug. 15, 2018 $ / shares	Jul. 30, 2018 $ / shares	May 15, 2018 $ / shares	Apr. 27, 2018 $ / shares	Feb. 15, 2018 $ / shares	Jan. 30, 2018 $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) ft²
Disposed of by Sale
Subsequent Event [Line Items]
Property square feet (in sqft) \| ft²														7,972,692
Gross sales price \| $												$ 1,031,286	$ 862,624	$ 1,300,000
Series D
Subsequent Event [Line Items]
Dividend declared (in dollars per share)					$ 0.40625		$ 0.40625		$ 0.40625		$ 0.40625
Dividends paid (in dollars per share)				$ 0.40625		$ 0.40625		$ 0.40625		$ 0.40625
Subsequent event \| 1735 Market Street \| Disposed of by Sale
Subsequent Event [Line Items]
Percentage of equity interests in fee simple owner		100.00%
Property square feet (in sqft) \| ft²		1,286,936
Gross sales price \| $		$ 451,600
Subsequent event \| Series D
Subsequent Event [Line Items]
Dividend declared (in dollars per share)			$ 0.40625
Dividends paid (in dollars per share)	$ 0.40625