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Organization and Summary of Significant Accounting Policies (Textual) (Details) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) | Dec. 31, 2018 shares | Dec. 31, 2018 | Dec. 31, 2018 Property | Dec. 31, 2018 States | Dec. 31, 2018 Communities | Dec. 31, 2018 ft²
Real Estate Properties |  |  |  |  |  |  |  |  |
Percentage Of Rental Revenue And Other Income From Leasing Of Apartment Homes | 93.00% |  |  |  |  |  |  |  |
Percentage of Rental Revenue and Other Income From Non-leasing Activities | 7.00% |  |  |  |  |  |  |  |
Loss Contingency Accrual | $ 8,700 | $ 32,100 |  |  |  |  |  |  |
General partners' capital account, units outstanding | shares |  | 113,643,166 |  | 113,844,267 |  |  |  |  |
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest | 96.50% | 96.40% |  |  |  |  |  |  |
Number of Real Estate Properties |  |  |  |  |  | 303 |  | 303 |
Advertising expenses | $ 20,200 | $ 18,800 | $ 13,000 |  |  |  |  |  |
Number of States in which Entity Operates | States |  |  |  |  |  |  | 17 |  |
Minimum |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Percentage of ownership interests of all consolidated subsidiaries (percent) |  |  |  |  | 92.50% |  |  |  |
Maximum |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Percentage of ownership interests of all consolidated subsidiaries (percent) |  |  |  |  | 100.00% |  |  |  |
Development Properties |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Number of Real Estate Properties | Communities |  |  |  |  |  |  |  | 3 |
Number of units under development community | Property |  |  |  |  |  | 577 |  |  |
Development Properties | Expected Costs |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Development and capital improvements in progress | 118,500 |  |  |  |  |  |  |  |
Development Properties | Costs Incurred to Date |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Development and capital improvements in progress | 30,900 |  |  |  |  |  |  |  |
Retail |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Number of Real Estate Properties | Property |  |  |  |  |  | 30 |  |  |
Square footage of real estate property (square foot) | ft² |  |  |  |  |  |  |  |  | 615,000
Commercial Properties |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Number of Real Estate Properties | Property |  |  |  |  |  | 4 |  |  |
Square footage of real estate property (square foot) | ft² |  |  |  |  |  |  |  |  | 260,000
Post Massachusetts Avenue |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  | 35.00% |  |  |  |
Real Estate Investments, Joint Ventures | 44,200 |  |  |  |  |  |  |  |
Real Estate Technology Ventures, L.P. [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  | 20.70% |  |  |  |
Real Estate Investments, Joint Ventures | 3,800 |  |  |  |  |  |  |  |
Real Estate Technology Ventures, L.P. [Member] | Limited Partner Capital Contribution, Future Obligation [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Real Estate Investments, Joint Ventures | 13,600 |  |  |  |  |  |  |  |
Post River North [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Number of units in real estate property |  |  |  |  | 359 |  |  |  |
Buildings, Improvements, and Other | 70,500 |  |  |  |  |  |  |  |
Percentage of ownership interests of all consolidated subsidiaries (percent) |  |  |  |  | 92.50% |  |  |  |
Land | 14,900 |  |  |  |  |  |  |  |
Accrued Liabilities | 1,200 |  |  |  |  |  |  |  |
Parent Company [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Net Cash Provided by (Used in) Operating Activities | 734,292 | 660,800 | 485,004 |  |  |  |  |  |
Capitalized Development Costs, Period | 4,200 | 11,000 | 2,700 |  |  |  |  |  |
Development and capital improvements in progress | 59,506 | 116,833 |  |  |  |  |  |  |
Buildings, Improvements, and Other | 11,670,216 | 11,281,504 |  |  |  |  |  |  |
Total interest capitalized during period | 2,047 | 7,238 | 2,073 |  |  |  |  |  |
Lease Intangibles, Gross | 13,598,550 | 13,234,754 |  |  |  |  |  |  |
Depreciation and amortization | 489,759 | 493,708 | 322,958 |  |  |  |  |  |
Land | 1,868,828 | 1,836,417 |  |  |  |  |  |  |
Accrued Liabilities | 413,850 | 405,560 |  |  |  |  |  |  |
Net Cash Provided by (Used in) Investing Activities | (366,350) | (294,210) | (649,131) |  |  |  |  |  |
Net Cash Provided by (Used in) Financing Activities | (405,136) | (399,523) | 222,286 |  |  |  |  |  |
Accrued Liabilities [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Dividends Payable | 113,200 | 108,700 |  |  |  |  |  |  |
Accrued Real Estate Taxes | 123,500 | 99,600 |  |  |  |  |  |  |
Unearned Income | 41,100 | 40,800 |  |  |  |  |  |  |
Loss Contingency, Loss in Period |  | 32,100 |  |  |  |  |  |  |
Security Deposit Liability | 18,700 | 19,100 |  |  |  |  |  |  |
Interest Payable | 15,100 | 18,100 |  |  |  |  |  |  |
Limited Partner [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Net Cash Provided by (Used in) Operating Activities | 734,292 | $ 660,800 | 485,004 |  |  |  |  |  |
General partners' capital account, units outstanding | shares |  | 113,643,166 |  | 113,844,267 |  |  |  |  |
Development and capital improvements in progress | 59,506 | $ 116,833 |  |  |  |  |  |  |
Buildings, Improvements, and Other | 11,670,216 | 11,281,504 |  |  |  |  |  |  |
Total interest capitalized during period | 2,047 | 7,238 | 2,073 |  |  |  |  |  |
Lease Intangibles, Gross | 13,598,550 | 13,234,754 |  |  |  |  |  |  |
Depreciation and amortization | 489,759 | 493,708 | 322,958 |  |  |  |  |  |
Land | 1,868,828 | 1,836,417 |  |  |  |  |  |  |
Accrued Liabilities | 413,850 | 405,560 |  |  |  |  |  |  |
Net Cash Provided by (Used in) Investing Activities | (366,350) | (294,210) | (649,131) |  |  |  |  |  |
Net Cash Provided by (Used in) Financing Activities | (405,136) | (399,523) | 222,286 |  |  |  |  |  |
Water Utility Revenue [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Property Management Fee Revenue | 39,100 | 38,300 | 31,100 |  |  |  |  |  |
Cable Utility Revenue [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Property Management Fee Revenue | 29,800 | 30,400 | 31,600 |  |  |  |  |  |
Accounting Standards Update 2016-15 [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Net Cash Provided by (Used in) Operating Activities |  | 1,900 | 600 |  |  |  |  |  |
Net Cash Provided by (Used in) Investing Activities |  | 200 | 500 |  |  |  |  |  |
Net Cash Provided by (Used in) Financing Activities |  | 1,700 | 100 |  |  |  |  |  |
Accounting Standards Update 2016-18 [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Net Cash Provided by (Used in) Operating Activities |  | 400 | 300 |  |  |  |  |  |
Net Cash Provided by (Used in) Investing Activities |  | 10,600 | 61,900 |  |  |  |  |  |
Restricted Cash and Cash Equivalents |  | 78,100 | $ 88,300 |  |  |  |  |  |
Accounting Standards Update 2016-02 [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Operating Lease, Right-of-Use Asset | 43,000 |  |  |  |  |  |  |  |
Operating Lease, Liability | 33,000 |  |  |  |  |  |  |  |
Leases, Acquired-in-Place [Member] |  |  |  |  |  |  |  |  |
Real Estate Properties |  |  |  |  |  |  |  |  |
Lease Intangibles, Gross | $ 3,900 | $ 7,100 |  |  |  |  |  |  |

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