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Employee Plans - Additional Information (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Value of common shares that can be acquired by the employee and trustees under employees share purchase plan | $ 100,000 |  |
Number of common shares authorized after amendment | 7,000,000 |  |
Common Shares available for purchase under the ESPP | 2,837,877 |  |
Purchase price of common stock | 85.00% |  |
Maximum eligible compensation percentage for the defined contribution plan (the 401(k) Plan) | 4.00% |  |
Defined contribution plan vesting period | 5 years |  |
Defined contribution plan, compensation expense | $ 4,600,000 | $ 4,900,000 | $ 5,500,000
Highly Compensated Employees [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Maximum eligible compensation percentage for the defined contribution plan (the 401(k) Plan) | 3.00% |  |

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- Definition Description of the period of time over which an employee's right to contribution plus actual earnings is no longer contingent on satisfaction of a service condition. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition Represents the maximum amount of an employee's contribution to the defined contribution plan that is matched by the company. + References No definition available. + Details
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Namespace Prefix: | eqr_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the number of common shares available for purchase under the employee share purchase plan at the balance sheet date. + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Represents the maximum value of common shares an employee can acquire under the employee share purchase plan on an annual basis. + References No definition available. + Details
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Balance Type: | debit
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- Definition Represents the number of shares authorized for purchase under the employee share purchase plan after the most recent amendment. + References No definition available. + Details
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Namespace Prefix: | eqr_
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Period Type: | instant

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Discount rate from fair value on purchase date that participants pay for shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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