Earnings Per Share and Earnings Per Unit (Details 1) (USD $) In Thousands, except Per Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Numerator for net income per Unit basic and diluted
Income (loss) from continuing operations	$ 21,195	$ (9,945)	$ 16,495	$ (29,153)
Net (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(71)	185	(31)	435
Discontinued operations, net	560,558	20,034	698,324	97,098
OPERATING PARTNERSHIP
Numerator for net income per Unit basic and diluted
Income (loss) from continuing operations	21,195	(9,945)	16,495	(29,153)
Net (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(71)	185	(31)	435
Allocation to Preference Units	(3,467)	(3,618)	(6,933)	(7,238)
Income (loss) from continuing operations available to Units	17,657	(13,378)	9,531	(35,956)
Discontinued operations, net	560,558	20,034	698,324	97,098
Numerator for net income per Unit - basic and diluted	578,215	6,656	707,855	61,142
Denominator for net income per Unit - basic and diluted
Denominator for net income per Unit- basic	307,954	295,898	307,106	295,177
Effect of dilutive securities:
Dilution for Units issuable upon assumed exercise/vesting of EQR's long-term compensation award shares/units	$ 4,245		$ 4,274
Denominator for net income per Unit - diluted	312,199	295,898	311,380	295,177
Net income per Unit - basic	$ 1.875	$ 0.022	$ 2.302	$ 0.207
Net income per Unit - diluted	$ 1.852	$ 0.022	$ 2.273	$ 0.207
Net income per Unit - basic:
Income from continuing operations available to Units	$ 0.057	$ (0.045)	$ 0.031	$ (0.121)
Discontinued operations, net	$ 1.818	$ 0.067	$ 2.271	$ 0.328
Net income per Unit - basic	$ 1.875	$ 0.022	$ 2.302	$ 0.207
Net income per Unit - diluted
Income from continuing operations available to Units	$ 0.057	$ (0.045)	$ 0.031	$ (0.121)
Discontinued operations, net	$ 1.795	$ 0.067	$ 2.242	$ 0.328
Net income per Unit - diluted	$ 1.852	$ 0.022	$ 2.273	$ 0.207

Amount of net (income) loss for the period allocated to noncontrolling partners in partially owned properties.

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Capital impact of aggregate cash stock and paid-in-kind dividends declared for preference units during the periods.

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Effect of dilutive securities.

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The amount of income or loss from continuing operations, available to each outstanding limited partnership and general partnership unit in a publicly traded limited partnership or master limited partnership (MLP) during the reporting period.

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This element represents the income or loss from continuing operations attributable to the economic entity which may be defined as revenue less expenses and taxes from ongoing operations before extraordinary items and cumulative effects of changes in accounting principles.

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The amount of net income (loss) from discontinued operations available to each unit outstanding and each unit that would have been outstanding assuming the issuance of units for all dilutive potential units outstanding.

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The amounts resulting from the "as-if" assumption that units were converted for purposes of computing the dilutive effect of convertible securities.

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Net income after adjustments for dividends on preference units.

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Net income loss per outstanding limited partnership and general partnership unit.

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Weighted Average Number Of Limited Partnership And General Partnership Unit Outstanding.

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The average number of units issued and outstanding that are used in calculating diluted earnings per unit determined based on the timing of issuance of units in the period.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, and noncontrolling interest.

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This element represents the overall income (loss) from a disposal group that is classified as a component of the entity, net of income tax, reported as a separate component of income before extraordinary items before deduction or consideration of the amount which may be allocable to noncontrolling interests, if any. Includes the following (net of tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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The amount of income (loss) from disposition of discontinued operations available to each limited partnership and general partnership unit during the reporting period, net of tax.

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Net income (loss) allocated to each outstanding limited partnership and general partnership unit.

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Weighted average number of limited partnership and general partnership units outstanding determined by relating the portion of time within a reporting period that limited partnership and general partnership units have been outstanding to the total time in that period. Includes, for example, the number of units distributed to unit holders whereby unit holders have the ability to elect to receive the unit holders' entire distribution in cash or units of equivalent value or there is a potential limitation on the total amount of cash that all unit holders can elect to receive in aggregate.

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