Annual report pursuant to Section 13 and 15(d)

Properties, net (Details 4)

v3.6.0.2
Properties, net (Details 4)
ft² in Thousands, $ in Thousands
 12 Months Ended
Jul. 21, 2016
USD ($)
Dec. 31, 2016
USD ($)
ft²
buillding
Dec. 31, 2015
USD ($)
ft²
buillding
Dec. 31, 2014
USD ($)
ft²
buillding
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 a redeemable noncontrolling interest in a joint venture   $ 22,600 $ 0 $ 0
Proceeds from sale of land held-for-investment   21,800    
Gains on sale of other land   $ 7,200    
Operating properties, net [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Number of Buildings | buillding   21 9 8
Total Rentable Square Feet | ft²   1,577 1,597 303
Transaction Value   $ 248,738 $ 347,785 $ 28,835
Gain on Disposition   $ 15,871 $ 64,033 $ 5,093
Operating properties, net [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    
Transaction Value   $ 142,800    
Gain on Disposition   $ 4,742    
Operating properties, net [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    
Transaction Value   $ 2,400    
Gain on Disposition   $ 0    
Operating properties, net [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    
Transaction Value   $ 14,513    
Gain on Disposition   $ 1,906    
Operating properties, net [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    
Transaction Value   $ 5,200    
Gain on Disposition   $ 0    
Operating properties, net [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    
Transaction Value   $ 2,900    
Gain on Disposition   $ 848    
Operating properties, net [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    
Transaction Value   $ 48,100    
Gain on Disposition   $ 8,375    
Operating properties, net [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    
Transaction Value   $ 2,625    
Gain on Disposition   $ 0    
Operating properties, net [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    
Transaction Value   $ 7,800    
Gain on Disposition   $ 0    
Operating properties, net [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    
Transaction Value   $ 12,100    
Gain on Disposition   $ 0    
Operating properties, net [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    
Transaction Value   $ 10,300    
Gain on Disposition   $ 0    
Operating office properties [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Total Rentable Square Feet | ft²   17,200    
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 a redeemable noncontrolling interest 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, net [Member] | Data Center Shells [Member]        
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Gain on Disposition   $ 17,900    
Number of properties contributed | buillding   6