Debt Instrument, Debt Default, Interest

No definition available.

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- Definition

Debt Instrument, Extension Option Fee, Percent

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Number of Extension Options

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Term, Extension Option

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility, Accordion Feature, Increase Limit

+ References

No definition available.

+ Details

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Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the number of buildings secured by mortgage notes.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of properties secured by mortgage notes.

+ References

No definition available.

+ Details

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Namespace Prefix:	eqc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Details

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Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 50

-Section 40

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12317-112629

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 50

-Section 40

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=49170532&loc=d3e12355-112629

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(d))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Indebtedness - Narrative (Details) (USD $)	3 Months Ended		12 Months Ended	9 Months Ended	0 Months Ended
Indebtedness - Narrative (Details) (USD $)	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Mar. 31, 2015	Jan. 29, 2015 option	Jan. 28, 2015
Debt Instrument [Line Items]
Loss on early extinguishment of debt	$ 428,000	$ 0
Real estate properties, net	4,633,227,000us-gaap_RealEstateInvestmentPropertyNet		4,697,998,000us-gaap_RealEstateInvestmentPropertyNet	4,633,227,000us-gaap_RealEstateInvestmentPropertyNet
Mortgage notes payable, net	606,423,000us-gaap_SecuredDebt		609,249,000us-gaap_SecuredDebt	606,423,000us-gaap_SecuredDebt
Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	750,000,000.0			750,000,000.0
Basis points on variable rate			1.50%
Commitment fee percentage			0.35%
Unsecured term loan, due December 2016
Debt Instrument [Line Items]
Outstanding indebtedness						400,000,000
Basis points on variable rate			1.85%
Loan facility, 5-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000			200,000,000
Loan facility, 7-year term
Debt Instrument [Line Items]
Term loan amount outstanding	200,000,000			200,000,000
Revolving credit facility and term loans
Debt Instrument [Line Items]
Additional increases in maximum amount of borrowings available					1,150,000,000.00
Mortgage notes maturing from 2015 through 2026
Debt Instrument [Line Items]
Number of real estate properties secured by mortgage	10			10
Number of buildings secured by mortgage	14			14
Real estate properties, net	700,800,000			700,800,000
Mortgage notes payable, net	606,400,000			606,400,000
225 Water Street in Jacksonville, Florida \| Mortgage notes maturing from 2015 through 2026
Debt Instrument [Line Items]
Outstanding indebtedness	40,100,000			40,100,000
Interest accrual rate				10.03%
Default interest				4.00%
Revolving credit facility
Debt Instrument [Line Items]
Debt instrument, number of extension options					2
Debt instrument, extension option term					6 months
Debt instrument, extension option fee, percent					0.075%
Interest rate payable percentage	1.43%
Amount outstanding	0			0
Amount available for borrowing	750,000,000			750,000,000
Revolving credit facility \| Unsecured revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity					750,000,000.0
Revolving credit facility \| Loan facility, 5-year term
Debt Instrument [Line Items]
Term loan amount outstanding					200,000,000
Debt instrument, term					5 years
Interest rate payable percentage	1.58%
Revolving credit facility \| Loan facility, 7-year term
Debt Instrument [Line Items]
Term loan amount outstanding					200,000,000
Debt instrument, term					7 years
Interest rate payable percentage	1.98%
Minimum \| Revolving credit facility
Debt Instrument [Line Items]
Commitment fee percentage					0.125%
Maximum \| Revolving credit facility
Debt Instrument [Line Items]
Commitment fee percentage					0.30%
LIBOR \| Minimum \| Loan facility, 5-year term
Debt Instrument [Line Items]
Basis points on variable rate					0.90%
LIBOR \| Minimum \| Loan facility, 7-year term
Debt Instrument [Line Items]
Basis points on variable rate					1.40%
LIBOR \| Minimum \| Revolving credit facility
Debt Instrument [Line Items]
Basis points on variable rate					0.875%
LIBOR \| Maximum \| Loan facility, 5-year term
Debt Instrument [Line Items]
Basis points on variable rate					1.80%
LIBOR \| Maximum \| Loan facility, 7-year term
Debt Instrument [Line Items]
Basis points on variable rate					2.35%
LIBOR \| Maximum \| Revolving credit facility
Debt Instrument [Line Items]
Basis points on variable rate					1.55%
Base rate \| Minimum \| Revolving credit facility
Debt Instrument [Line Items]
Basis points on variable rate					0.00%
Base rate \| Maximum \| Revolving credit facility
Debt Instrument [Line Items]
Basis points on variable rate					0.55%
Line of Credit \| Revolving credit facility
Debt Instrument [Line Items]
Maximum borrowing capacity					100,000,000.0