Quarterly report pursuant to Section 13 or 15(d)

Real Estate - Variable Interest Entities (Details)

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Real Estate - Variable Interest Entities (Details) (USD $)
0 Months Ended 0 Months Ended
Jun. 15, 2011
Jun. 15, 2011
Six Fifty North Glebe Road [Member]
Mar. 31, 2013
Six Fifty North Glebe Road [Member]
Dec. 31, 2012
Six Fifty North Glebe Road [Member]
Nov. 23, 2011
First Street 1225 [Member]
Mar. 31, 2013
First Street 1225 [Member]
Dec. 31, 2012
First Street 1225 [Member]
Real Estate Properties [Line Items]              
Estimated development costs   $ 49,900,000     $ 95,300,000    
Percentage of capital contribution through debt 70.00% 70.00%     70.00%    
Variable interest entity, qualitative or quantitative information, ownership percentage   90.00%     95.00%    
Percentage of residential property to be leased to achieve project stabilization stage   90.00%          
Noncontrolling interest, ownership percentage by noncontrolling owners   10.00%     5.00%    
Land and capitalized development costs related to joint ventures     17,616,000 15,646,000   21,561,000 19,807,000
Accounts payable and accrued liabilities related to joint ventures     $ 875,000 $ 115,000   $ 952,000 $ 1,676,000