Organization and Basis of Presentation (Details)	Mar. 31, 2013 sqft
Summary of stabilized portfolio of operating properties
Rentable square feet	320,398
Office Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	116
Rentable square feet	13,570,059
Number of Tenants	553
Percentage Occupied	90.30%
Lease Up Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	2
Rentable square feet	508,000
Development Properties [Member]
Summary of stabilized portfolio of operating properties
Number of buildings	4	[1]
Rentable square feet	1,416,000	[1]

[1] Estimated rentable square feet upon completion.