Quarterly report pursuant to Section 13 or 15(d)

Fair Value Disclosures - Financial Assets and Liabilities Not Measured at Fair Value (Details)

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Fair Value Disclosures - Financial Assets and Liabilities Not Measured at Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Estimate of Fair Value, Fair Value Disclosure [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash and cash equivalents, Fair Value $ 16,743 $ 19,324
Restricted Cash, Fair Value Disclosure 10,804 14,582
Mortgage notes payable, Fair Value 341,230 374,591
Lines of credit payable, Fair Value 70,000 0
Notes payable, Fair Value 895,303 968,040
Estimate of Fair Value, Fair Value Disclosure [Member] | 2445 M Street Note Receivable [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
2445 M Street note receivable, Fair Value 7,413 6,654
Carrying (Reported) Amount, Fair Value Disclosure [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Mortgage notes payable, Fair Value 312,396 342,970
Notes payable, Fair Value 846,323 906,190
Carrying (Reported) Amount, Fair Value Disclosure [Member] | 2445 M Street Note Receivable [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
2445 M Street note receivable, Fair Value $ 6,804 $ 6,617