Nature of Business and Financial Statement Presentation - Additional Information (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Total real estate assets, net	$ 6,992,664,000	$ 6,968,394,000
Variable Interest Entity, Primary Beneficiary [Member]
Significant Accounting Policies [Line Items]
Total real estate assets, net	189,500,000	184,600,000
Mortgages	21,000,000	21,500,000
Other real estate liabilities	$ 1,200,000	$ 1,900,000