Organization and Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2012 RSF NumberofBuildings
Summary of stabilized portfolio of operating properties
Number of Buildings	7
Rentable square feet	374,139
Office Properties [Member]
Summary of stabilized portfolio of operating properties
Number of Buildings	7
Rentable square feet	374,139
Stabilized Portfolio [Member]
Summary of stabilized portfolio of operating properties
Number of Buildings	150
Rentable square feet	15,211,172
Number of Tenants	500
Percentage Occupied	91.60%
Stabilized Portfolio [Member] | Office Properties [Member]
Summary of stabilized portfolio of operating properties
Number of Buildings	111	[1]
Rentable square feet	11,797,818	[1]
Number of Tenants	440	[1]
Percentage Occupied	90.00%	[1]
Stabilized Portfolio [Member] | Non-Reportable Segment - Industrial Properties [Member]
Summary of stabilized portfolio of operating properties
Number of Buildings	39
Rentable square feet	3,413,354
Number of Tenants	60
Percentage Occupied	97.00%

[1] Includes seven office properties acquired in one transaction during the three months ended March 31, 2012 encompassing 374,139 rentable square feet (see Note 2 for additional information).