Fair Value Measurements (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended		12 Months Ended		3 Months Ended	0 Months Ended	12 Months Ended				3 Months Ended				12 Months Ended				3 Months Ended		12 Months Ended				12 Months Ended	3 Months Ended		12 Months Ended						12 Months Ended				12 Months Ended		3 Months Ended
	Apr. 28, 2011	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2012 Notes Receivable From Real Estate Joint Ventures And Partnerships [Member]	Apr. 28, 2011 Subordinate Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Subordinate Tax Increment Revenue Bonds [Member]		Dec. 31, 2010 Subordinate Tax Increment Revenue Bonds [Member]	Apr. 28, 2011 Senior Tax Increment Revenue Bonds [Member]	Mar. 31, 2012 Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Subordinate Tax Increment Revenue Bonds [Member]	Mar. 31, 2012 Significant Unobservable Inputs (Level 3) [Member] Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Tax Increment Revenue Bonds [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] 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] 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]	Mar. 31, 2012 Minimum [Member] Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Minimum [Member] Significant Unobservable Inputs (Level 3) [Member] Subordinate Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Minimum [Member] Impaired Property [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Minimum [Member] Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2012 Maximum [Member] Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Maximum [Member] Significant Unobservable Inputs (Level 3) [Member] Subordinate Tax Increment Revenue Bonds [Member]	Dec. 31, 2011 Maximum [Member] Impaired Property [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Maximum [Member] Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2012 Debt [Member] Minimum [Member]	Mar. 31, 2012 Debt [Member] Maximum [Member]
Fair Value Measurements [Line Items]
Property, net		$ 3,696,192,000	[1]	$ 3,702,236,000	[1]											$ 135,500,000
Property fair value																98,596,000		389,000	98,207,000
Cost to sell property																				800,000		2,000,000
Subordinated tax increment revenue bonds at cost							22,400,000
Investments								26,723,000					26,723,000	26,505,000	26,505,000
Cash received on exchange of bonds	16,500,000
Total Gains (Losses)		(9,779,000)	[2]	(71,195,000)	[3]			(18,737,000)	[3]	(11,700,000)						(36,907,000)	[3]			(3,171,000)	[2]	(13,799,000)	[3]				(6,608,000)	[2]	(1,752,000)	[3]
Property held for sale, net		414,413,000		73,241,000																42,200,000		57,000,000
Property held for sale fair value																				39,791,000		45,157,000		39,791,000	43,657,000	1,500,000
Investment in real estate joint ventures and partnerships, net		338,332,000		341,608,000																							30,800,000		8,100,000
Investment in real estate joint ventures and partnerships																											24,231,000		6,311,000		24,231,000	6,311,000
Subordinated bonds received on exchange of bonds							57,700,000
Investment at fair value							$ 10,700,000				$ 51,300,000
Discount rates used in fair value determination						2.74%						7.50%														10.00%									8.00%				13.00%		1.40%	6.40%
Capitalization rates used in fair value determination																																				7.00%				9.00%
Expected future growth rates																																	1.00%	1.00%			4.00%	4.00%
Expected inflation rates																																	1.00%	1.00%			2.00%	2.00%

[1] Consolidated Variable Interest Entities' Assets and Liabilities included in the above balances (See Note 17):

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

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