Annual report pursuant to Section 13 and 15(d)

Properties, Net (Details 4)

v3.10.0.1
Properties, Net (Details 4)
ft² in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
USD ($)
ft²
Property
Dec. 31, 2018
USD ($)
ft²
Property
Dec. 31, 2017
USD ($)
ft²
Property
Dec. 31, 2016
USD ($)
ft²
buillding
Property
Construction Activities [Line Items]        
Impairment losses | $   $ 2,367 $ 15,123 $ 101,391
Fort Meade/BW Corridor [Member]        
Construction Activities [Line Items]        
Impairment losses | $ $ 2,400      
Newly-constructed properties placed in service [Member]        
Construction Activities [Line Items]        
Square footage of real estate properties (in square feet) | ft² 666 666 1,100 639
Number of real estate properties 6 6 8 6
Newly-constructed properties placed in service, partially operational [Member]        
Construction Activities [Line Items]        
Number of real estate properties 2 2    
Newly redeveloped properties placed In service [Member]        
Construction Activities [Line Items]        
Square footage of real estate properties (in square feet) | ft² 22 22 94 61
Number of real estate properties 1 1   3
Properties Under Construction or Contractually Committed, Partially Operational [Member]        
Construction Activities [Line Items]        
Number of real estate properties 2 2    
Properties under Construction or Contractually Commited for Construction [Member]        
Construction Activities [Line Items]        
Square footage of real estate properties (in square feet) | ft² 1,100 1,100    
Number of real estate properties 9 9    
Properties under redevelopment [Member]        
Construction Activities [Line Items]        
Square footage of real estate properties (in square feet) | ft² 106 106    
Number of real estate properties 1 1