Acquisitions and Discontinued Operations (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
Business Acquisition [Line Items]
Land	$ 926,423	$ 928,025
Buildings and improvements	7,585,004	7,543,326
Total assets	7,422,495	7,506,554	7,615,480
Northgate Mall [Member]
Business Acquisition [Line Items]
Acquisition, purchase price	12,172
Land	1,217
Buildings and improvements	10,590
Above-market leases	243
In-place leases	365
Total assets	12,415
Below-market leases	(243)
Net assets acquired	$ 12,172

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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The net of assets and liabilities.

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The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

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This element represents the amount of value allocated by a lessor (acquirer) to lease agreements which exist at acquisition of a leased property. Such amount may include the value assigned to existing tenant relationships and excludes the market adjustment component of the value assigned for above or below-market leases acquired.

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Aggregate of the carrying amounts as of the balance sheet date of investments in building and building improvements.

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Carrying amount as of the balance sheet date of real estate held for productive use. This excludes land held for sale.

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