Organization of the Parent Company and The Operating Partnership (Details)	Mar. 31, 2015 sqft real_estate_investment	Mar. 31, 2014 sqft
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	24,900,000
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 [Line Items]
Net rentable square feet	6,700,000	5,700,000
Number Of Unconsolidated Real Estate Ventures	17
Wholly-owned Management Company Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	33,700,000
Third Parties and Real Estate Ventures [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	8,900,000
Total Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	198
Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	161
Industrial Facilities [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	20
Mixed Use Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	5
Retail Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	1
Core Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	187
Assets Held-for-sale [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	6
Development Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	3
Redevelopment Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	1
Re-entitlement Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	1
Wholly Owned Properties [Member] | Parent Company [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	24,800,000