Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Revenue Recognition and Accounts Receivable and Allowance (Details)

v2.4.0.6
Summary of Significant Accounting Policies - Revenue Recognition and Accounts Receivable and Allowance (Details) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Accounting Policies [Line Items]        
Stated interest rate   3.875%    
Operating Lease Term, Average, Minimum 3 years      
Operating Lease Term, Average, Maximum 5 years      
Rents and other receivables, allowance for doubtful accounts $ 10,958,000 $ 8,683,000 $ 7,259,000 $ 5,137,000
Allowance for Doubtful Accounts Receivable 3,800,000 3,800,000 3,400,000  
Write-offs of Accounts Receivable 1,500,000 2,400,000 1,200,000  
Notes receivable, net 7,297,000 7,348,000    
2445 M Street [Member]
       
Accounting Policies [Line Items]        
Notes receivable, net $ 6,617,000 $ 6,975,000