Annual report pursuant to Section 13 and 15(d)

Properties, Net (Details 5)

v3.10.0.1
Properties, Net (Details 5)
ft² in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Jul. 21, 2016
USD ($)
Property
Dec. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
ft²
buillding
Dec. 31, 2016
USD ($)
ft²
buillding
Oct. 27, 2017
USD ($)
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 contributed into a joint venture     $ 0 $ 0 $ 22,600  
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 contributed into a joint venture $ 147,600          
Initial amount borrowed         60,000  
Ownership percentage 50.00%          
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  
Gains on sale of other land       4,200 7,200  
Operating properties [Member] | Single-tenant data centers [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          
Operating properties [Member] | Held-for-sale [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]            
Undiscounted indemnification amount           $ 20,000
Gain on Sale   $ 1,500        
Total Rentable Square Feet | ft²           193
Transaction Value           $ 44,000
Operating properties [Member] | Disposed of by sale [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Gain on Sale       $ 5,636 $ 15,871  
Number of Buildings | buillding       12 21  
Total Rentable Square Feet | ft²       799 1,577  
Transaction Value       $ 125,829 $ 248,738  
Operating properties [Member] | Disposed of by sale [Member] | Regional Office [Member] | Arborcrest Corporate Campus [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Gain on Sale         $ 4,742  
Number of Buildings | buillding         4  
Total Rentable Square Feet | ft²         654  
Transaction Value         $ 142,800  
Operating properties [Member] | Disposed of by sale [Member] | Regional Office [Member] | 8003 Corporate Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Gain on Sale         $ 0  
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         18  
Transaction Value         $ 2,400  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 1,906  
Number of Buildings | buillding         5  
Total Rentable Square Feet | ft²         130  
Transaction Value         $ 14,513  
Operating properties [Member] | Disposed of by sale [Member] | Regional Office [Member] | 4940 Campbell Drive [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Gain on Sale         $ 0  
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         50  
Transaction Value         $ 5,200  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 848  
Number of Buildings | buillding         2  
Total Rentable Square Feet | ft²         25  
Transaction Value         $ 2,900  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 8,375  
Number of Buildings | buillding         3  
Total Rentable Square Feet | ft²         299  
Transaction Value         $ 48,100  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 0  
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         29  
Transaction Value         $ 2,625  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 0  
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         101  
Transaction Value         $ 7,800  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale       $ 0    
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       190    
Transaction Value       $ 39,000    
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 0  
Number of Buildings | buillding         1  
Total Rentable Square Feet | ft²         151  
Transaction Value         $ 12,100  
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale       $ 0    
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       37    
Transaction Value       $ 2,300    
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale       $ 831    
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       57    
Transaction Value       $ 7,529    
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale       $ 3,625    
Number of Buildings | buillding       1    
Total Rentable Square Feet | ft²       103    
Transaction Value       $ 29,500    
Operating properties [Member] | Disposed of by sale [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]            
Gain on Sale         $ 0  
Number of Buildings | buillding         2  
Total Rentable Square Feet | ft²         120  
Transaction Value         $ 10,300  
Operating properties [Member] | Disposed of by sale [Member] | White Marsh, Maryland [Member] | Regional Office and Other [Member]            
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]            
Gain on Sale       $ 1,180    
Number of Buildings | buillding       8    
Total Rentable Square Feet | ft²       412    
Transaction Value       $ 47,500