Annual report pursuant to Section 13 and 15(d)

Properties, net (Details 6)

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Properties, net (Details 6)
 12 Months Ended
Dec. 31, 2011
property
sqfeet
Dec. 31, 2010
sqfeet
property
Newly-constructed properties placed in service
    
Construction and Redevelopment Activities    
Number of real estate properties placed into service 7 9
Square feet placed in service on properties during the period (in square feet) 566,000 816,000
Newly-constructed properties placed in service | Baltimore/Washington Corridor
    
Construction and Redevelopment Activities    
Number of real estate properties placed into service 3 3
Newly-constructed properties placed in service | Greater Baltimore
    
Construction and Redevelopment Activities    
Number of real estate properties placed into service 2 2
Newly-constructed properties placed in service | San Antonio
    
Construction and Redevelopment Activities    
Number of real estate properties placed into service 1 2
Newly-constructed properties placed in service | St. Mary's County
    
Construction and Redevelopment Activities    
Number of real estate properties placed into service 1  
Newly-constructed properties placed in service | Colorado Springs
    
Construction and Redevelopment Activities    
Number of real estate properties placed into service   2
Properties under construction
    
Construction and Redevelopment Activities    
Number of real estate properties 6  
Square footage of real estate properties (in square feet) 789,000  
Properties under construction | Baltimore/Washington Corridor
    
Construction and Redevelopment Activities    
Number of real estate properties 3  
Properties under construction | Greater Baltimore
    
Construction and Redevelopment Activities    
Number of real estate properties 1  
Properties under construction | Northern Virginia
    
Construction and Redevelopment Activities    
Number of real estate properties 1  
Properties under construction | Huntsville
    
Construction and Redevelopment Activities    
Number of real estate properties 1  
Properties under redevelopment
    
Construction and Redevelopment Activities    
Square footage of real estate properties (in square feet) 113,000  
Properties under redevelopment | Greater Philadelphia
    
Construction and Redevelopment Activities    
Number of real estate properties 1