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Basis of Presentation and Principles of Consolidation and Significant Accounting Policies - Additional Information (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) ft² Property Community State ApartmentUnit shares	Jun. 30, 2018 shares	Jun. 30, 2021 Property	Dec. 31, 2020 Property	Jun. 30, 2020 Property	Dec. 31, 2019 Property	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($) shares
Real Estate Properties [Line Items]
General Partners' Capital Account, Units Outstanding | shares	114,043,089	113,808,292
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest	96.50%	96.50%
Number of owned or owned interests of apartment communities | Property	303
Development and capital improvements in progress	$ 97,526							$ 59,506
Number of States in which Entity Operates | State	17
Buildings, Improvements, and Other	$ 11,775,716							11,670,216
Land	1,883,960							1,868,828
Accrued expenses and other liabilities	450,212							$ 413,850
Operating Lease, Right-of-Use Asset	53,500
Operating Lease, Liability	$ 33,234
Operating Lease, Weighted Average Remaining Lease Term	32 years
Operating Lease, Weighted Average Discount Rate, Percent	4.40%
Percentage Of Rental Revenue From Leasing Of Apartment Homes	93.00%
Percentage Of Reimbursable Revenue From Leasing Of Apartment Homes	6.00%
Percentage of Rental Revenue and Other Income From Non-leasing Activities	1.00%
Accounting Standards Update 2016-02 [Member]
Real Estate Properties [Line Items]
Operating Lease, Right-of-Use Asset							$ 54,300
Operating Lease, Liability							$ 33,600
Operating Lease, Weighted Average Remaining Lease Term							33 years
Operating Lease, Weighted Average Discount Rate, Percent							4.40%
Post Massachusetts Avenue [Member]
Real Estate Properties [Line Items]
Number of apartments included in a community | Community	1
Real Estate Investments, Joint Ventures	$ 44,000
Post Massachusetts Avenue [Member] | Apartment LLC [Member]
Real Estate Properties [Line Items]
Equity Method Investment, Ownership Percentage	35.00%
Real Estate Technology Ventures, L.P. [Member]
Real Estate Properties [Line Items]
Equity Method Investment, Ownership Percentage	20.70%
Real Estate Investments, Joint Ventures	$ 10,900
Real Estate Technology Ventures, L.P. [Member] | Other Assets [Member]
Real Estate Properties [Line Items]
Real Estate Investments, Joint Ventures	$ 6,200
Post River North [Member]
Real Estate Properties [Line Items]
Percentage Of Ownership Interests	92.50%
Number of apartments included in a community | ApartmentUnit	359
Buildings, Improvements, and Other	$ 69,100
Land	14,900
Accrued expenses and other liabilities	$ 800
Percentage of remaining ownership interests	7.50%
Phoenix Midtown [Member]
Real Estate Properties [Line Items]
Percentage Of Ownership Interests	80.00%
Buildings, Improvements, and Other	$ 8,700
Land	9,400
Accrued expenses and other liabilities	$ 2,000
Percentage of remaining ownership interests	20.00%
Minimum [Member]
Real Estate Properties [Line Items]
Percentage Of Ownership Interests	80.00%
Maximum [Member]
Real Estate Properties [Line Items]
Percentage Of Ownership Interests	100.00%
Maximum [Member] | Accounting Standards Update 2016-02 [Member]
Real Estate Properties [Line Items]
Operating lease, term of contract	1 year
Limited Partner [Member]
Real Estate Properties [Line Items]
General Partners' Capital Account, Units Outstanding | shares	114,043,089							113,844,267
Number of owned or owned interests of apartment communities | Property	1
Development and capital improvements in progress	$ 97,526							$ 59,506
Buildings, Improvements, and Other	11,775,716							11,670,216
Land	1,883,960							1,868,828
Accrued expenses and other liabilities	$ 450,212							$ 413,850
Limited Partner [Member] | Minimum [Member]
Real Estate Properties [Line Items]
Percentage Of Ownership Interests	80.00%
Limited Partner [Member] | Maximum [Member]
Real Estate Properties [Line Items]
Percentage Of Ownership Interests	100.00%
Retail
Real Estate Properties [Line Items]
Number of owned or owned interests of apartment communities | Property	30
Square Footage of Real Estate Property | ft²	615,000
Development Properties
Real Estate Properties [Line Items]
Number of owned or owned interests of apartment communities | Community	5
Number of units under development community | Property	1,090
Development and capital improvements in progress	$ 230,500
Development and capital improvements in progress	$ 82,500
Development Properties | Expected Costs [Member]
Real Estate Properties [Line Items]
Number of owned or owned interests of apartment communities | Community	5
Development Properties | Scenario Forecast [Member]
Real Estate Properties [Line Items]
Number of owned or owned interests of apartment communities | Property			1	1	1	2
Commercial Real Estate [Member]
Real Estate Properties [Line Items]
Number of owned or owned interests of apartment communities | Property	4
Square Footage of Real Estate Property | ft²	260,000

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Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing, equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases. Also includes amount of investment in certain other real estate investments not specifically identified elsewhere in the existing taxonomy.

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