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Organization of The Parent Company and The Operating Partnership (Textual) (Details) - Jun. 30, 2017 ft² in Millions | Total | property | ft² | Real_Estate_Investment | a | Apartment_unit
--- | --- | --- | --- | --- | --- | ---
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 99 |  |  |  |
Office Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 87 |  |  |  |
Mixed Use Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 6 |  |  |  |
Retail Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 1 |  |  |  |
Core Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 94 |  |  |  |
Development Property [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 2 |  |  |  |
Redevelopment Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Properties | property |  | 3 |  |  |  |
Unconsolidated Real Estate Ventures [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment |  |  |  | 13 |  |
Unconsolidated Real Estate Ventures [Member] | Seven Real Estate Ventures [Member] | Office Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment |  |  |  | 7 |  |
Rentable Square Feet |  |  | 8.1 |  |  |
Unconsolidated Real Estate Ventures [Member] | Four Real Estate Ventures [Member] | Land Held For Development [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment |  |  |  | 4 |  |
Acreage of land | a |  |  |  |  | 5.7 |
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower One [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment |  |  |  | 1 |  |
Number of Property units |  | 345 |  |  |  | 345
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower Two [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment |  |  |  | 1 |  |
Number of Property units |  | 321 |  |  |  | 321
Parent Company [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Ownership in the Operating Partnership | 99.20% |  |  |  |  |
Net Rentable Square Feet |  |  | 16.4 |  |  |
Area Owned by Company of Undeveloped Parcels of Land | a |  |  |  |  | 278 |
Area of Additional Undeveloped Parcels of Land With Option to Purchase | a |  |  |  |  | 60 |
Total Potential Development Capacity |  |  | 11.2 |  |  |
Parent Company [Member] | Assets Held-for-sale [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Acreage of land | a |  |  |  |  | 50 |
Total Potential Development Capacity |  |  | 0.4 |  |  |
Wholly-owned Management Company Subsidiaries [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Net Rentable Square Feet |  |  | 26.6 |  |  |
Wholly-owned Management Company Subsidiaries [Member] | Partially Owned Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Net Rentable Square Feet |  |  | 10.2 |  |  |
Wholly-owned Management Company Subsidiaries [Member] | Wholly Owned Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Net Rentable Square Feet |  |  | 16.4 |  |  |
Wholly-owned Management Company Subsidiaries [Member] | Office and Industrial Properties [Member] | Partially Owned Properties [Member] |  |  |  |  |  |
Organization of The Parent Company and The Operating Partnership [Line Items] |  |  |  |  |  |
Net Rentable Square Feet |  |  | 10.2 |  |  |

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