Fair Value Measurements (Assets Measured On Nonrecurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended						12 Months Ended				12 Months Ended				3 Months Ended		12 Months Ended						3 Months Ended		12 Months Ended
	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2012 Quoted Prices In Active Markets For Identical Assets And Liabilities (Level1) [Member]	Mar. 31, 2012 Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Subordinate Tax Increment Revenue Bonds [Member]		Dec. 31, 2010 Subordinate Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Subordinate Tax Increment Revenue Bonds [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Impaired Property [Member]		Dec. 31, 2011 Impaired Property [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Impaired Property [Member] Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2012 Impaired Property Held For Sale [Member]		Dec. 31, 2011 Impaired Property Held For Sale [Member]		Mar. 31, 2012 Impaired Property Held For Sale [Member] Quoted Prices In Active Markets For Identical Assets And Liabilities (Level1) [Member]	Mar. 31, 2012 Impaired Property Held For Sale [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Impaired Property Held For Sale [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Impaired Property Held For Sale [Member] Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2012 Impaired Investment In Real Estate Joint Ventures And Partnerships [Member]		Dec. 31, 2011 Impaired Investment In Real Estate Joint Ventures And Partnerships [Member]		Mar. 31, 2012 Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] Quoted Prices In Active Markets For Identical Assets And Liabilities (Level1) [Member]	Mar. 31, 2012 Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Property													$ 98,596		$ 389	$ 98,207
Property held for sale																	39,791		45,157			39,791	43,657	1,500
Investment in real estate joint ventures and partnerships																									24,231		6,311			24,231	6,311
Investments									26,723			26,723
Total	64,022		176,787			64,022	44,046	132,741
Total Gains (Losses)	$ (9,779)	[1]	$ (71,195)	[2]					$ (18,737)	[2]	$ (11,700)		$ (36,907)	[2]			$ (3,171)	[1]	$ (13,799)	[2]					$ (6,608)	[1]	$ (1,752)	[2]

[1] Total gains (losses) exclude impairments on disposed assets because they are no longer held by us.

[2] Total gains (losses) are reflected throughout 2011 and exclude impairments on disposed assets because they are no longer held by us.