Organization of the Parent Company and The Operating Partnership Organization of the Parent Company and The Operating Partnership (Details)	Sep. 30, 2013
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the Operating Partnership	98.80%
Parent Company [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	24,100,000
Area Owned By Company Of Undeveloped Parcels Of Land	423
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	6,200,000
Number Of Unconsolidated Real Estate Ventures	18
Wholly-owned Management Company Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	30,700,000
Third Parties and Real Estate Ventures [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net rentable square feet	6,600,000
Total Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	210
Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	182
Assets Held-for-sale [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	1
Industrial Facilities [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	19
Mixed Use Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	5
Development Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	1
Redevelopment Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	2
Re-entitlement Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Real Estate Properties	1

Organization of the Parent Company and The Operating Partnership Organization of the Parent Company and The Operating Partnership (Details)

Sep. 30, 2013

Organization of The Parent Company and The Operating Partnership [Line Items]

Ownership in the Operating Partnership

98.80%

Parent Company [Member]

Organization of The Parent Company and The Operating Partnership [Line Items]

Net rentable square feet

24,100,000

Area Owned By Company Of Undeveloped Parcels Of Land

423

Area Of Additional Undeveloped Parcels Of Land With Option to Purchase