Annual report pursuant to Section 13 and 15(d)

Properties, Net (Details 4)

v3.8.0.1
Properties, Net (Details 4)
$ in Thousands
 12 Months Ended
Jul. 21, 2016
USD ($)
Aug. 28, 2015
USD ($)
Dec. 31, 2017
USD ($)
ft²
buillding
Property
Dec. 31, 2016
USD ($)
ft²
buillding
Property
Dec. 31, 2015
USD ($)
ft²
buillding
Property
Oct. 27, 2017
USD ($)
ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Increase in property and redeemable noncontrolling interests in connection with property contribution by redeemable noncontrolling interests in a joint venture     $ 0 $ 22,600 $ 0  
(Loss) gain on early extinguishment of debt     $ (513) $ (1,110) $ 85,275  
Operating properties [Member] | 15000 and 15010 Conference Center Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Debt settled through the surrender of real estate assets   $ 150,000        
(Loss) gain on early extinguishment of debt   $ 84,800        
Newly-constructed properties placed in service [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     8 6 7  
Total Rentable Square Feet | ft²     1,100,000 639,000 897,000  
Newly redeveloped properties placed In service [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     3 3 2  
Total Rentable Square Feet | ft²     94,000 61,000 170,000  
Properties under construction or contractually committed for construction [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     9      
Total Rentable Square Feet | ft²     1,100,000      
Properties under redevelopment [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     1      
Total Rentable Square Feet | ft²     22,000      
Office properties under, or contractually committed for, construction or approved for redevelopment [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     10      
Total Rentable Square Feet | ft²     1,100,000      
Office properties under, or contractually committed for, construction or approved for redevelopment [Member] | Single-tenant data centers [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     3      
Office properties under, or contractually committed for, construction or approved for redevelopment [Member] | Properties completed Held-for-future lease [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | Property     2      
Operating office properties [Member] | Single-tenant data centers [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Transaction Value       $ 44,300    
Ownership percentage sold (percent) 50.00%          
Increase in property and redeemable noncontrolling interests in connection with property contribution by redeemable noncontrolling interests in a joint venture $ 147,600          
Initial amount borrowed       60,000    
Ownership percentage 50.00%          
Operating office properties [Member] | Single-tenant data centers [Member] | Operating properties [Member] | Data Center Shells [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Gain on Sale       $ 17,900    
Number of properties contributed | Property       6    
Held-for-sale [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Proceeds from sale of land held-for-investment     $ 14,300 $ 21,800 $ 18,100  
Gains on sale of other land     $ 4,200 $ 7,200 $ 4,000  
Held-for-sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Data Center Shells [Member] | 11751 Meadowville Lane [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Total Rentable Square Feet | ft²           193,000
Transaction Value           $ 44,000
Undiscounted indemnification amount           $ 20,000
Disposed of by sale [Member] | Operating properties [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding     12 21 9  
Total Rentable Square Feet | ft²     799,000 1,577,000 1,597,000  
Transaction Value     $ 125,829 $ 248,738 $ 347,785  
Gain on Sale     $ 5,636 $ 15,871 $ 64,033  
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | Arborcrest Corporate Campus [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       4    
Total Rentable Square Feet | ft²       654,000    
Transaction Value       $ 142,800    
Gain on Sale       $ 4,742    
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 8003 Corporate Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       18,000    
Transaction Value       $ 2,400    
Gain on Sale       $ 0    
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 8007, 8013, 8015, 8019 and 8023-8027 Corporate Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       5    
Total Rentable Square Feet | ft²       130,000    
Transaction Value       $ 14,513    
Gain on Sale       $ 1,906    
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 4940 Campbell Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       50,000    
Transaction Value       $ 5,200    
Gain on Sale       $ 0    
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 1550 Westbranch Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         160,000  
Transaction Value         $ 27,800  
Gain on Sale         $ 0  
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 13200 Woodland Park Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         397,000  
Transaction Value         $ 84,000  
Gain on Sale         $ 42,515  
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 9900, 9910, 9920 Franklin Square Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding         3  
Total Rentable Square Feet | ft²         135,000  
Transaction Value         $ 24,150  
Gain on Sale         $ 6,468  
Disposed of by sale [Member] | Operating properties [Member] | Regional Office [Member] | 9690 Deereco Road and 375 W Padonia Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding         2  
Total Rentable Square Feet | ft²         240,000  
Transaction Value         $ 44,500  
Gain on Sale         $ 15,050  
Disposed of by sale [Member] | Operating properties [Member] | Fort Meade/BW Corridor [Member] | 1341 and 1343 Ashton Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       2    
Total Rentable Square Feet | ft²       25,000    
Transaction Value       $ 2,900    
Gain on Sale       $ 848    
Disposed of by sale [Member] | Operating properties [Member] | Fort Meade/BW Corridor [Member] | 1302, 1304 & 1306 Concourse Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       3    
Total Rentable Square Feet | ft²       299,000    
Transaction Value       $ 48,100    
Gain on Sale       $ 8,375    
Disposed of by sale [Member] | Operating properties [Member] | Fort Meade/BW Corridor [Member] | 1331 Ashton Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       29,000    
Transaction Value       $ 2,625    
Gain on Sale       $ 0    
Disposed of by sale [Member] | Operating properties [Member] | Fort Meade/BW Corridor [Member] | 900 Elkridge Landing Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       101,000    
Transaction Value       $ 7,800    
Gain on Sale       $ 0    
Disposed of by sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Fort Meade/BW Corridor [Member] | 1334 Ashton Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding     1      
Total Rentable Square Feet | ft²     37,000      
Transaction Value     $ 2,300      
Gain on Sale     $ 0      
Disposed of by sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Fort Meade/BW Corridor [Member] | 7320 Parkway Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding     1      
Total Rentable Square Feet | ft²     57,000      
Transaction Value     $ 7,529      
Gain on Sale     $ 831      
Disposed of by sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Data Center Shells [Member] | 201 Technology Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding     1      
Total Rentable Square Feet | ft²     103,000      
Transaction Value     $ 29,500      
Gain on Sale     $ 3,625      
Disposed of by sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Northern Virginia Defense/IT [Member] | 3120 Fairview Park Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding     1      
Total Rentable Square Feet | ft²     190,000      
Transaction Value     $ 39,000      
Gain on Sale     $ 0      
Disposed of by sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Northern Virginia Defense/IT [Member] | 2900 Towerview Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       151,000    
Transaction Value       $ 12,100    
Gain on Sale       $ 0    
Disposed of by sale [Member] | Operating properties [Member] | Defense/Information Technology Sector [Member] | Northern Virginia Defense/IT [Member] | 15000 and 15010 Conference Center Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding         2  
Total Rentable Square Feet | ft²         665,000  
Transaction Value         $ 167,335  
Gain on Sale         $ 0  
Disposed of by sale [Member] | Operating properties [Member] | Other Segments [Member] | 1560 A and B Cable Ranch Road [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding       2    
Total Rentable Square Feet | ft²       120,000    
Transaction Value       $ 10,300    
Gain on Sale       $ 0    
White Marsh, Maryland [Member] | Disposed of by sale [Member] | Operating properties [Member] | Regional Office and Other [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Number of Buildings | buillding     8      
Total Rentable Square Feet | ft²     412,000      
Transaction Value     $ 47,500      
Gain on Sale     $ 1,180