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