Organization of The Parent Company and The Operating Partnership (Details)	Dec. 31, 2014 acre sqft
Parent Company [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Ownership in the Operating Partnership	99.00%
Net rentable square feet	25,100,000
Area Owned by Company of Undeveloped Parcels Of Land	415
Area of additional undeveloped parcels of land with option to purchase	63
Total potential development capacity	6,000,000
Unconsolidated real estate ventures [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of unconsolidated real estate ventures	17
Net rentable square feet	6,700,000
Wholly-owned management company subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Net rentable square feet	33,900,000
Third Parties and Unconsolidated Real Estate Ventures [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Net rentable square feet	8,900,000
Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Ownership in the Operating Partnership	100.00%
Total Properties [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	200
Office Properties [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	167
Industrial facilities [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	20
Mixed-use properties [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	5
Retail Properties [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	1
Core Properties [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	193
Development Property [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	3
Assets Held-for-sale [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	2
Redevelopment Property [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	1
Re-entitlement Property [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Number of properties with ownership interest	1
Wholly Owned Properties [Member] | Parent Company [Member]
Organization of The Parent Company and The Operating Partnership (Textuals) [Abstract]
Net rentable square feet	25,000,000