Annual report pursuant to Section 13 and 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
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
2445 M Street note receivable, carrying value $ 7,300 $ 8,100
Mortgage notes payable 427,710 361,860
Mortgage notes payable, fair value 463,238 380,360
Lines of credit payable, carrying value 99,000 100,000
Lines of credit payable, fair value 99,000 100,000
Notes payable, carrying value 657,470 753,587
Notes payable, fair value 713,797 785,637
2445 M Street Note Receivable [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
2445 M Street note receivable, carrying value 6,975 7,090
2445 M Street note receivable, fair value 7,721 8,048
Cash and cash equivalents, including restricted cash [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Cash and cash equivalents, including restricted cash, carrying value 32,189 99,253
Cash and cash equivalents, including restricted cash, fair value $ 32,189 $ 99,253