This element represents the number of buildings sold or agreed to be sold by the entity.

No definition available.

Name:	eqc_NumberOfBuildingsSold
Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the number of properties sold or agreed to be sold by the entity.

+ References

No definition available.

+ Details

Name:	eqc_NumberOfPropertiesSold
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

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

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=56944662&loc=d3e3602-108585

+ Details

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

- 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_A333LaurelOakDriveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Summary of Properties Sold (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended		1 Months Ended
	Jan. 31, 2013 building property	Mar. 31, 2015 sqft	Mar. 31, 2014 sqft	Mar. 31, 2015 building	Jan. 31, 2015 building property sqft
Real Estate Properties [Line Items]
Number of Properties	3eqc_NumberOfPropertiesSold
Number of Buildings	18eqc_NumberOfBuildingsSold
Square Footage (in sqft)		42,752,000us-gaap_AreaOfRealEstateProperty	42,913,000us-gaap_AreaOfRealEstateProperty	42,752,000us-gaap_AreaOfRealEstateProperty
Gain on Sale		$ 5,868us-gaap_GainLossOnSaleOfProperties	$ 0us-gaap_GainLossOnSaleOfProperties
333 Laurel Oak Drive \| Sale of properties resulting in gains
Real Estate Properties [Line Items]
Number of Buildings				3
Disposed of by Sale \| Sale of properties resulting in gains
Real Estate Properties [Line Items]
Number of Properties		2
Number of Buildings		3
Square Footage (in sqft)		167,274		167,274
Gross Sales Price		21,183
Gain on Sale		5,868
Disposed of by Sale \| 11350 North Meridian Street \| Sale of properties resulting in gains
Real Estate Properties [Line Items]
Number of Properties					1
Number of Buildings					1
Square Footage (in sqft)					72,264
Gross Sales Price					4,200
Gain on Sale					766
Disposed of by Sale \| 333 Laurel Oak Drive \| Sale of properties resulting in gains
Real Estate Properties [Line Items]
Number of Properties				0
Number of Buildings				1
Square Footage (in sqft)		27,164		27,164
Gross Sales Price				2,450
Gain on Sale				251
Disposed of by Sale \| 1921 E. Alton Avenue \| Sale of properties resulting in gains
Real Estate Properties [Line Items]
Number of Properties				1
Number of Buildings				1
Square Footage (in sqft)		67,846		67,846
Gross Sales Price				14,533
Gain on Sale				4,851