Annual report pursuant to Section 13 and 15(d)

Properties, net (Details 5)

v3.3.1.900
Properties, net (Details 5)
$ in Thousands
12 Months Ended
Aug. 28, 2015
USD ($)
Dec. 23, 2013
USD ($)
Dec. 31, 2015
USD ($)
ft²
Property
buillding
Dec. 31, 2014
USD ($)
ft²
Property
buillding
Dec. 31, 2013
USD ($)
ft²
Property
buillding
Dispositions          
Gain (loss) on early extinguishment of debt     $ 85,275 $ (9,552) $ (27,030)
Non-operating Properties [Member]          
Dispositions          
Gain on Disposition     4,000 5,600  
Sale price of non-operating properties     $ 18,100 $ 28,300 $ 3,500
Operating properties, net [Member]          
Dispositions          
Number of Buildings Disposed | buillding     9 8 31
Total Rentable Square Feet | ft²     1,597,000 302,958 2,345,000
Transaction value of operating property dispositions     $ 347,785 $ 28,835 $ 293,301
Gain on Disposition     $ 64,033 $ 5,093 $ 2,671
Operating properties, net [Member] | 1550 Westbranch Drive [Member]          
Dispositions          
Number of Buildings Disposed | buillding     1    
Total Rentable Square Feet | ft²     160,000    
Transaction value of operating property dispositions     $ 27,800    
Gain on Disposition     $ 0    
Operating properties, net [Member] | 15000 and 15010 Conference Center Drive [Member]          
Dispositions          
Number of Buildings Disposed | buillding     2    
Total Rentable Square Feet | ft²     665,000    
Transaction value of operating property dispositions     $ 167,335    
Gain on Disposition     $ 0    
Operating properties, net [Member] | 13200 Woodland Park Road [Member]          
Dispositions          
Number of Buildings Disposed | buillding     1    
Total Rentable Square Feet | ft²     397,000    
Transaction value of operating property dispositions     $ 84,000    
Gain on Disposition     $ 42,515    
Operating properties, net [Member] | 9900, 9910, 9920 Franklin Square Drive [Member]          
Dispositions          
Number of Buildings Disposed | buillding     3    
Total Rentable Square Feet | ft²     135,000    
Transaction value of operating property dispositions     $ 24,150    
Gain on Disposition     $ 6,468    
Operating properties, net [Member] | 9690 Deereco Road and 375 W Padonia Road [Member]          
Dispositions          
Number of Buildings Disposed | buillding     2    
Total Rentable Square Feet | ft²     240,000    
Transaction value of operating property dispositions     $ 44,500    
Gain on Disposition     $ 15,050    
Operating properties, net [Member] | 4969 and 4979 Mercantile Rd [Member]          
Dispositions          
Number of Buildings Disposed | buillding       2  
Total Rentable Square Feet | ft²       96,721  
Transaction value of operating property dispositions       $ 5,960  
Gain on Disposition       $ 2,124  
Operating properties, net [Member] | 9930 and 9940 Franklin Square [Member]          
Dispositions          
Number of Buildings Disposed | buillding       2  
Total Rentable Square Feet | ft²       71,992  
Transaction value of operating property dispositions       $ 10,475  
Gain on Disposition       $ 2,303  
Operating properties, net [Member] | 5020, 5022, 5024 and 5026 Campbell Boulevard [Member]          
Dispositions          
Number of Buildings Disposed | buillding       4  
Total Rentable Square Feet | ft²       134,245  
Transaction value of operating property dispositions       $ 12,400  
Gain on Disposition       666  
Operating properties, net [Member] | 920 Elkridge Landing Road [Member]          
Dispositions          
Number of Buildings Disposed | buillding         1
Total Rentable Square Feet | ft²         103,000
Transaction value of operating property dispositions         $ 6,900
Gain on Disposition         $ 0
Operating properties, net [Member] | 4230 Forbes Boulevard [Member]          
Dispositions          
Number of Buildings Disposed | buillding         1
Total Rentable Square Feet | ft²         56,000
Transaction value of operating property dispositions         $ 5,600
Gain on Disposition         $ 1,507
Operating properties, net [Member] | December 2013 Colorado Springs Portfolio Disposition [Member]          
Dispositions          
Number of Buildings Disposed | buillding         15
Total Rentable Square Feet | ft²         1,165,000
Transaction value of operating property dispositions         $ 133,925
Gain on Disposition         $ 1,164
Operating properties, net [Member] | December 2013 Portfolio Conveyance [Member]          
Dispositions          
Number of Buildings Disposed | buillding         14
Total Rentable Square Feet | ft²         1,021,000
Transaction value of operating property dispositions         $ 146,876
Gain on Disposition         $ 0
Greater Philadelphia [Member]          
Dispositions          
Depreciation Expense Resulting From Useful Life Change       $ 12,900  
15000 and 15010 Conference Center Drive [Member] | Northern Virginia [Member] | Operating properties, net [Member]          
Dispositions          
Debt settled through the surrender of real estate assets $ 150,000        
Gain (loss) on early extinguishment of debt $ 84,800        
December 2013 Portfolio Conveyance [Member] | Operating properties, net [Member]          
Dispositions          
Debt settled through the surrender of real estate assets   $ 146,500      
Gain (loss) on early extinguishment of debt   $ 67,800      
Newly-constructed properties placed in service [Member]          
Dispositions          
Square Feet of Properties Placed in Service | ft²     897,000 692,000 812,000
Number of real estate properties | Property     7 5 8
Newly Redeveloped Properties Placed In Service [Member] | Greater Philadelphia and St. Mary's County, Maryland [Member]          
Dispositions          
Square Feet of Properties Placed in Service | ft²     170,000    
Number of real estate properties | Property     2    
Properties under Construction or Contractually Commited for Construction [Member]          
Dispositions          
Total Rentable Square Feet | ft²     1,300,000    
Number of real estate properties | Property     9    
Properties under redevelopment [Member]          
Dispositions          
Total Rentable Square Feet | ft²     156,000    
Number of real estate properties | Property     4