Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended					12 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Interest Rate Cap [Member] derivative_instruments	Dec. 31, 2012 Interest Rate Cap [Member] derivative_instruments	Sep. 30, 2013 Interest Rate Swap [Member] derivative_instruments	Dec. 31, 2012 Interest Rate Swap [Member] derivative_instruments	Sep. 30, 2013 Citadel Mall [Member] Consolidated Revenue [Member]	Sep. 30, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2012 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Sep. 30, 2013 Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2012 Significant Other Observable Inputs (Level 2) [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments held				1	1	4	4
Assets:
Fair value of available-for-sale securities		$ 14,556	$ 27,679						$ 14,556	$ 16,556	$ 0	$ 0	$ 0	$ 11,123
Cost Method Investments, Fair Value Disclosure			2,475							0		0		2,475
Liabilities:
Interest rate swaps		4,417	5,805								4,417	5,805
Long-term Debt, Fair Value		5,069,679	5,058,411
Mortgage and other indebtedness		4,867,717	4,745,683
Available-for-sale Securities, Debt Maturities, Date	Oct. 01, 2028
Assumed Reduction In Cash Flows Used To Calculate Fair Value Of Cost Method Investment			0% to 10%
Assumed Capitalization Rate Range in Determining Fair Value			10% to 12%
Discount Rate Used To Calculate Fair Value Of Privately Held Debt And Equity Securities			20.00%
Concentration risk								0.60%
Assumed Capitalization Rate Range Used To Determine Fair Value		10% to 12%
Holding period		10 years
Asset Impairment Charges		$ 585
Estimated sales cost		1.00%