Quarterly report pursuant to Section 13 or 15(d)

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

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Real Estate - Held for Sale and Sold Properties (Details)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
ft²
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
apartment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Real estate impairment $ 1,886 $ 0  
Braddock Metro Center [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Rentable Square Feet | ft² 356,000    
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Braddock Metro Center [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Real estate impairment     $ 9,100
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | M Street 2445 [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Contract Sales Price $ 100,000    
Real estate impairment $ 1,900   24,100
Office [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | M Street 2445 [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Rentable Square Feet | ft² 292,000    
2018 Properties Sold Group [Member] | Office [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Braddock Metro Center [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
2017 Properties Sold Group [Member] | Multifamily [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Walker House [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Number of Units | apartment     212
Contract Sales Price     $ 32,200
Gain on Sale     $ 23,838