Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details 3)

v3.6.0.2
Fair Value Measurements (Details 3)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2016
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Property
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Fair value of impaired properties and other assets              
Impairment losses         $ 101,391 $ 23,289 $ 1,416
Assets held for sale, net $ 94,654       94,654 96,782  
Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Assets held for sale, net 94,654       94,654 96,782  
Fort Meade/BW Corridor [Member]              
Fair value of impaired properties and other assets              
Number of properties | Property       2      
Fair value measurement on a nonrecurring basis [Member] | Operating properties, net [Member]              
Fair value of impaired properties and other assets              
Impairment losses             $ 1,400
Fair value measurement on a nonrecurring basis [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses   $ 11,500   $ 2,400      
Assets held for sale, net 94,700 161,500 $ 300,600 $ 225,900 94,700 96,800  
Fair Values on Measurement Date 79,685       79,685    
Fair value measurement on a nonrecurring basis [Member] | Held-for-sale [Member] | Fair Value, Inputs, Level 3 [Member]              
Fair value of impaired properties and other assets              
Fair Values on Measurement Date 79,685       $ 79,685    
Fair value measurement on a nonrecurring basis [Member] | Disposed of by sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses 300            
Transaction value of operating property dispositions 54,100 210,700          
Fair value measurement on a nonrecurring basis [Member] | Northern Virginia Defense/IT and Fort Meade/Baltimore Washington Corridor [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses     14,100        
Fair value measurement on a nonrecurring basis [Member] | Defense/Information Technology Sector [Member] | Northern Virginia Defense/IT [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses   13,300          
Fair value measurement on a nonrecurring basis [Member] | Aberdeen, Maryland [Member] | Land in development or held for future development [Member]              
Fair value of impaired properties and other assets              
Impairment losses     4,400        
Fair value measurement on a nonrecurring basis [Member] | Aberdeen, Maryland [Member] | Operating properties, net [Member] | Land in development or held for future development [Member]              
Fair value of impaired properties and other assets              
Impairment losses           6,600  
Fair value measurement on a nonrecurring basis [Member] | Aberdeen, Maryland [Member] | Other Segments [Member] | Operating properties, net [Member]              
Fair value of impaired properties and other assets              
Impairment losses     34,400        
Fair value measurement on a nonrecurring basis [Member] | Frederick, Maryland [Member] | Land in development or held for future development [Member]              
Fair value of impaired properties and other assets              
Impairment losses     8,200        
Fair value measurement on a nonrecurring basis [Member] | Greater Philadelphia [Member] | Regional Office [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses     6,200        
Fair value measurement on a nonrecurring basis [Member] | Colorado Springs, Colorado and White Marsh, Maryland [Member] | Regional Office [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses     $ 2,400        
Fair value measurement on a nonrecurring basis [Member] | Colorado Springs [Member] | Held-for-sale [Member] | Land in development or held for future development [Member]              
Fair value of impaired properties and other assets              
Impairment losses           12,800  
Fair value measurement on a nonrecurring basis [Member] | White Marsh, Maryland [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses $ 1,300 10,000          
Fair value measurement on a nonrecurring basis [Member] | White Marsh, Maryland [Member] | Held-for-sale [Member] | Land in development or held for future development [Member]              
Fair value of impaired properties and other assets              
Impairment losses   $ 2,900          
Fair value measurement on a nonrecurring basis [Member] | White Marsh, Maryland [Member] | Regional Office [Member] | Held-for-sale [Member]              
Fair value of impaired properties and other assets              
Impairment losses           2,600  
Fair value measurement on a nonrecurring basis [Member] | Northern Virginia [Member] | Regional Office [Member] | Held-for-sale [Member] | Operating properties, net [Member]              
Fair value of impaired properties and other assets              
Impairment losses           $ 1,300