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Business Combinations (Textual) (Details) $ / shares in Units, ft² in Thousands |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 01, 2016 USD ($) ft² Communities properties $ / shares shares | Dec. 31, 2017 USD ($) shares | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) shares | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) shares | Dec. 31, 2015 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Business Combinations, Other Consideration | $ 2,000,000 |  |  |  |  |  |  |  |  |  |  |
Business Combination, Merger and Integration Related Expenses |  |  |  |  |  |  |  |  |  |  | $ 40,800,000 |
Redeemable Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Embedded Derivative, Fair Value of Embedded Derivative Asset | 14.24 |  |  |  |  |  |  |  |  |  |  |
Mandatorily Redeemable Preferred Stock, Fair Value Disclosure | $ 77 |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Outstanding | shares | 867,846 |  |  |  |  |  |  |  |  |  |  |
Unsecured Debt |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Consideration Transferred, Other | $ 300,000,000 |  |  |  |  |  |  |  |  |  |  |
Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Consideration Transferred, Other | $ 162,000,000 |  |  |  |  |  |  |  |  |  |  |
Equity Method Investments [Member] | Post [Member] [Domain] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number Of Units Acquired In Real Estate Property | Communities | 269 |  |  |  |  |  |  |  |  |  |  |
Development Portfolio [Member] | Post [Member] [Domain] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number Of Units Acquired In Real Estate Property | Communities | 2,262 |  |  |  |  |  |  |  |  |  |  |
Parent Company [Member] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest in Joint Ventures |  | $ 2,306,000 |  |  |  | $ 2,306,000 |  |  |  | $ 2,306,000 | 2,306,000 |
Total operating revenues |  | $ 382,738,000 | $ 384,550,000 | $ 382,791,000 | $ 378,908,000 | $ 307,198,000 | $ 276,898,000 | $ 272,236,000 | $ 269,016,000 | 1,528,987,000 | 1,125,348,000 | $ 1,042,779,000
Business Combination, Merger and Integration Related Expenses |  |  |  |  |  |  |  |  |  | $ 19,990,000 | $ 40,823,000 | $ 0
Preferred Stock, Shares Outstanding | shares |  | 867,846 |  |  |  | 867,846 |  |  |  | 867,846 | 867,846 |
Parent Company [Member] | Post [Member] [Domain] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of Apartment Communities Acquired in Real Estate Property | Communities | 61 |  |  |  |  |  |  |  |  |  |  |
Number Of Units Acquired In Real Estate Property | Communities | 24,138 |  |  |  |  |  |  |  |  |  |  |
Number of Commercial Properties Acquired in Real Estate Property | properties | 4 |  |  |  |  |  |  |  |  |  |  |
Acquired properties, purchase price | $ (4,006,586,000) |  |  |  |  |  |  |  |  |  |  |
Share Price | $ / shares | $ 91.41 |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, Acquisitions | shares | 38,000,000 |  |  |  |  |  |  |  |  |  |  |
Parent Company [Member] | Commercial | Post [Member] [Domain] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Square footage of real estate property (square foot) | ft² | 232 |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, Acquisitions | shares | 80,000 |  |  |  |  |  |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Domain] |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Merger and Integration Related Expenses |  |  |  |  |  |  |  |  |  | $ 20,000,000 |  |

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