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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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