Nature of Business and Financial Statement Presentation (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Total real estate assets for which the Company is deemed to be the primary beneficiary	$ 6,693,849	$ 6,719,063
Mortgage and other secured indebtedness	1,372,694	1,322,445
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Total real estate assets for which the Company is deemed to be the primary beneficiary	268,400	289,500
Mortgage and other secured indebtedness	22,600	23,500
Other liabilities	$ 1,200	$ 28,700