Organization and Ownership (Details)	Dec. 31, 2012 sqft
Summary of stabilized portfolio of operating properties
Rentable square feet	13,249,780	[1]
Office Properties [Member]
Summary of stabilized portfolio of operating properties
Rentable square feet	13,249,780	[1]
Development Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	0
Rentable square feet	1,416,000	[2]
Redevelopment Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	0
Rentable square feet	410,000	[2]
Lease Up Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	1
Rentable square feet	98,000	[2]
Stabilized Portfolio [Member] | Office Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	114
Rentable square feet	13,249,780
Number of Tenants	530
Percentage Occupied	92.80%

[1] Includes square footage from our stabilized portfolio.

[2] Estimated rentable square feet upon completion.