Organization of The Parent Company and The Operating Partnership (Textual) (Details)	Sep. 30, 2016	Sep. 30, 2016 property	Sep. 30, 2016 ft²	Sep. 30, 2016 Real_Estate_Investment	Sep. 30, 2016 a	Sep. 30, 2016 Apartment_unit	Feb. 04, 2016 property
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		117
Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		99
Rentable Square Feet | ft²			5,082,963
Mixed Use Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		7
Retail Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		1
Core Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		107
Development Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		4
Redevelopment Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		2
Assets Held-for-sale [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		4
Assets Held-for-sale [Member] | Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		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				14
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 | ft²			8,000,000
Unconsolidated Real Estate Ventures [Member] | Two Real Estate Ventures [Member] | Undeveloped Land [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment				2
Acreage of land | a					4.3
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Under Active Development Land [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment				2
Acreage of land | a					1.4
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
Number of Unconsolidated Investments in Real Estate Ventures		1
Unconsolidated Real Estate Ventures [Member] | One Real Estate Venture [Member] | Apartment Complex [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		398				398
MAP Venture [Member] | Industrial Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties		4					20
Parent Company [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the Operating Partnership	99.10%
Net Rentable Square Feet | ft²			17,800,000
Area Owned by Company of Undeveloped Parcels of Land | a					317
Area of Additional Undeveloped Parcels of Land With Option to Purchase | a					60
Total Potential Development Capacity | ft²			12,300,000
Wholly-owned Management Company Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net Rentable Square Feet | ft²			28,700,000
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 | ft²			10,900,000
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 | ft²			17,800,000
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 | ft²			10,900,000