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Nature of Business and Financial Statement Presentation - Additional Information (Detail) (USD $)
Sep. 30, 2013
Dec. 31, 2012
Significant Accounting Policies [Line Items]    
Total real estate assets, net $ 7,139,441,000 $ 6,968,394,000
Variable Interest Entity, Primary Beneficiary [Member]
   
Significant Accounting Policies [Line Items]    
Total real estate assets, net 186,300,000 184,600,000
Mortgages 19,400,000 21,500,000
Other real estate liabilities $ 1,800,000 $ 1,900,000