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Consolidation and Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Thousands | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($) shares | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($) shares | Sep. 30, 2017 Property | Sep. 30, 2017 States | Sep. 30, 2017 $ / shares | Sep. 30, 2017 Communities | Sep. 30, 2017 USD ($) | Sep. 30, 2017 shares | Sep. 30, 2017 ft² | Dec. 31, 2016 USD ($) $ / shares
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
General Partners' Capital Account, Units Outstanding | shares |  | 75,542,583 |  | 75,542,583 |  |  |  |  |  | 113,627,014 |  |
Limited Liability (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest |  |  | 96.40% |  |  |  |  |  |  |  |  |
Preferred Stock, Dividend Rate, Percentage |  |  | 8.50% |  |  |  |  |  |  |  |  |
Number of owned or owned interests of apartment communities |  |  |  |  | 303 |  |  | 302 |  |  |  |
Number of states in which apartment units are located | States |  |  |  |  |  | 17 |  |  |  |  |  |
Percentage Of Ownership Interests | 100.00% |  | 100.00% |  |  |  |  |  |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage Of Ownership Interests | 92.50% |  | 92.50% |  |  |  |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage Of Ownership Interests | 100.00% |  | 100.00% |  |  |  |  |  |  |  |  |
Development Properties [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of owned or owned interests of apartment communities | Communities |  |  |  |  |  |  |  | 5 |  |  |  |
Number of units under development community | Property |  |  |  |  | 1,434 |  |  |  |  |  |  |
Development Properties [Member] | Expected Costs [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Development and capital improvements in progress |  |  |  |  |  |  |  |  | $ 305,000 |  |  |
Development Properties [Member] | Costs Incurred to Date [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Development and capital improvements in progress |  |  |  |  |  |  |  |  | 235,300 |  |  |
Retail |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of owned or owned interests of apartment communities | Property |  |  |  |  | 29 |  |  |  |  |  |  |
Square Footage of Real Estate Property | ft² |  |  |  |  |  |  |  |  |  |  | 600,000 |
Commercial Real Estate [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Square Footage of Real Estate Property | ft² |  |  |  |  |  |  |  |  |  |  | 232,000 |
Real Estate Technology Ventures, L.P. [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 32.00% |  | 32.00% |  |  |  |  |  |  |  |  |
Real Estate Investments, Joint Ventures |  |  |  |  |  |  |  |  | 800 |  |  |
Real Estate Technology Ventures, L.P. [Member] | Limited Partner Capital Contribution, Future Obligation [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Investments, Joint Ventures |  |  |  |  |  |  |  |  | 14,200 |  |  |
Post River North [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of apartments included in a community | 358 |  | 358 |  |  |  |  |  |  |  |  |
Development and capital improvements in progress |  |  |  |  |  |  |  |  | 60,300 |  |  |
Percentage Of Ownership Interests | 92.50% |  | 92.50% |  |  |  |  |  |  |  |  |
Land |  |  |  |  |  |  |  |  | 14,500 |  |  |
Accrued expenses and other liabilities |  |  |  |  |  |  |  |  | 6,200 |  |  |
Post Massachusetts Avenue [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 35.00% |  | 35.00% |  |  |  |  |  |  |  |  |
Real Estate Investments, Joint Ventures |  |  |  |  |  |  |  |  | 45,100 |  |  |
Parent Company [Member] |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Par or Stated Value Per Share | $ / shares |  |  |  |  |  |  | $ 0.01 |  |  |  |  | $ 0.01
Merger Related Expenses | $ 128 | $ 3,901 | $ 3,977 | $ 3,901 |  |  |  |  |  |  |  |
Development and capital improvements in progress |  |  |  |  |  |  |  |  | 156,938 |  |  | $ 231,224
Land |  |  |  |  |  |  |  |  | 1,828,637 |  |  | 1,816,008
Accrued expenses and other liabilities |  |  |  |  |  |  |  |  | $ 439,662 |  |  | $ 414,244

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