v2.4.1.9

Organization (Details) (USD $)	12 Months Ended			0 Months Ended
Organization (Details) (USD $)	Dec. 31, 2014 apartment building project community	Dec. 31, 2013	Dec. 31, 2012	Apr. 01, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General partner ownership interest (in hundredths)	96.70%	94.60%
Noncontrolling interest Operating Partnership	3.30%	5.40%
Operating Partnership units outstanding (in shares)	2,201,810	2,149,802
Redemption value of Operating Partnership units outstanding	$ 455,000,000	$ 309,000,000
Number of apartment communities owned	239ess_NumberOfApartmentCommunitiesOwned
Apartment units owned	57,455ess_AggregateApartmentUnitsOwned
Ownership interests, number of commercial buildings	4
Ownership interests, number of active development projects	12
Business Acquisition [Line Items]
Merger and integration expenses	53,530,000	4,284,000	0
Share Price				$ 174us-gaap_SharePrice
Share Price After Deducting Special Dividend And Cash Consideration				$ 164
BRE Properties, Inc. [Member]
Business Acquisition [Line Items]
Common shares conversion ratio in connection with merger				0.2971
Share price (in dollars per share)				$ 7.18
Merger and integration expenses	$ 53,500,000			$ 4,300,000,000
Special Dividend Declared Per Share				$ 5.15
Cash Consideration Per Share Before Special Dividend				$ 12.33
Stock Issued During Period, Shares, Acquisitions				23,100,000
Share Price				$ 61
Share Price After Deducting Special Dividend And Cash Consideration				$ 48.67

Aggregate number of apartment units owned as of the balance sheet date.

+ References

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- Definition

Cash Consideration Per Share Before Special Dividend

+ References

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- Definition

Noncontrolling interest in Operating Partnership, which includes the Operating Partnership's vested long term incentive plan units and cumulative redeemable preferred units.

+ References

No definition available.

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- Definition

The number of apartment communities owned as of the balance sheet date.

+ References

No definition available.

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- Definition

Operating partnership units owned by noncontrolling interest partners, including Long Term Incentive Plan Units which convert to Partnership units.

+ References

No definition available.

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- Definition

The number of active development projects in which the company has an ownership interest.

+ References

No definition available.

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- Definition

The number of commercial buildings in which the company has an ownership interest.

+ References

No definition available.

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- Definition

Description of redemption value of total operating partnership units.

+ References

No definition available.

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- Definition

Share Price After Deducting Special Dividend And Cash Consideration

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- Definition

Special Dividend Declared Per Share

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No definition available.

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- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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- Definition

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

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-Publisher FASB

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Price of a single share of a number of saleable stocks of a company.

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No definition available.

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- Definition

Number of shares of stock issued during the period pursuant to acquisitions.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

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