Quarterly report pursuant to Section 13 or 15(d)

Real Estate - Held for Sale and Sold Properties (Details)

v3.19.1
Real Estate - Held for Sale and Sold Properties (Details)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
ft²
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
ft²
Dec. 31, 2017
USD ($)
Apr. 22, 2019
USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Real estate impairment $ 8,374 $ 1,886      
M Street 2445 [Member] | Office Building [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Real estate impairment     $ 1,900 $ 24,100  
Quantico Corporate Center [Member] | Office Building [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Rentable Square Feet | ft² 272,000        
Real estate impairment $ 8,400        
Quantico Corporate Center [Member] | Office Building [Member] | Subsequent Event          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Contract Sales Price         $ 33,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | M Street 2445 [Member] | Office Building [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Initial contracted sales price   100,000      
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | 2018 Properties Sold Group [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Contract Sales Price   $ 101,600      
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | 2018 Properties Sold Group [Member] | Office Building [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Rentable Square Feet | ft²     648,000    
Contract Sales Price     $ 194,600    
Gain on Sale     $ 2,495    
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | 2018 Properties Sold Group [Member] | Braddock Metro Center [Member] | Office Building [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Rentable Square Feet | ft²     356,000    
Contract Sales Price     $ 93,000    
Gain on Sale     $ 0    
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | 2018 Properties Sold Group [Member] | M Street 2445 [Member] | Office Building [Member]          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Rentable Square Feet | ft²     292,000