Organization of the Parent Company and The Operating Partnership Organization of the Parent Company and The Operating Partnership (Details)	Mar. 31, 2013 acre
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the Operating Partnership	98.70%
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land	24
Parent Company [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	24,300,000
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land	431
Area Of Additional Undeveloped Parcels Of Land With Option to Purchase	51
Total potential development capacity	6,100,000
Unconsolidated Real Estate Ventures [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	6,400,000
Number Of Unconsolidated Real Estate Ventures	19
Wholly-owned Management Company Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	31,100,000
Third Parties and Real Estate Ventures [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	6,800,000
Total Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	214
Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	185
Industrial Facilities [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	19
Mixed Use Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	5
Development Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	1
Redevelopment Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	2
Re-entitlement Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of properties with ownership interest	2