Fair Value Measurements (Narrative) (Details) (USD $)	0 Months Ended	9 Months Ended		12 Months Ended
	Apr. 28, 2011	Sep. 30, 2011		Dec. 31, 2010
Fair Value Measurements [Line Items]
Property, net		$ 3,751,334,000	[1]	$ 3,806,545,000	[1]
Notes receivable from real estate joint ventures and partnerships		149,814,000		184,788,000
Notes receivable from real estate joint ventures and partnerships, fair value		155,400,000		188,000,000
Cash received on exchange of bonds	16,500,000
Property Held for Sale, net		122,360,000
Investment in Real Estate Joint Ventures and Partnerships, net		342,672,000		347,526,000
As To Interest Rate [Member]
Fair Value Measurements [Line Items]
Fixed-rate debt		2,059,010,000		2,349,802,000
Variable-rate debt		546,727,000		239,646,000
Minimum [Member] | Subordinate Tax Increment Revenue Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Expected future growth rates		1.00%
Expected inflation rates		1.00%
Minimum [Member] | Impaired Property [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Discount rates used in fair value determination		8.00%
Minimum [Member] | Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Capitalization rates used in fair value determination		7.00%
Maximum [Member] | Subordinate Tax Increment Revenue Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Expected future growth rates		4.00%
Expected inflation rates		2.00%
Maximum [Member] | Impaired Property [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Discount rates used in fair value determination		13.00%
Maximum [Member] | Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Capitalization rates used in fair value determination		9.00%
Impaired Property [Member]
Fair Value Measurements [Line Items]
Property, net		128,500,000
Property fair value		94,551,000		2,325,000
Impairment losses related to property		33,853,000	[2]	2,827,000	[2]
Impaired Property [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Measurements [Line Items]
Property fair value		389,000
Impaired Property [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Property, net				5,100,000
Property fair value		94,162,000		2,325,000
Impaired Property Held For Sale [Member]
Fair Value Measurements [Line Items]
Impairment losses related to property		14,845,000	[2]
Property held for sale fair value		54,921,000
Impaired Property Held For Sale [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Measurements [Line Items]
Cost to sell property		2,400,000
Property Held for Sale, net		67,300,000
Property held for sale fair value		54,921,000
Impaired Investment In Real Estate Joint Ventures And Partnerships [Member]
Fair Value Measurements [Line Items]
Impairment losses related to partially owned real estate joint ventures and partnerships		1,474,000	[2]
Investment in Real Estate Joint Ventures and Partnerships		6,033,000
Impaired Investment In Real Estate Joint Ventures And Partnerships [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Investment in Real Estate Joint Ventures and Partnerships, net		7,500,000
Investment in Real Estate Joint Ventures and Partnerships		6,033,000
Subordinate Tax Increment Revenue Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Measurements [Line Items]
Subordinated tax increment revenue bonds at cost				22,400,000
Investment at fair value				10,700,000
Investments		26,723,000
Significant Unobservable Inputs (Level 3) [Member] | Subordinate Tax Increment Revenue Note [Member]
Fair Value Measurements [Line Items]
Subordinated tax increment revenue bonds at cost				600,000
Investment at fair value				0
Subordinate Tax Increment Revenue Bonds [Member]
Fair Value Measurements [Line Items]
Carrying value of bonds				At December 31, 2010, the carrying value of these bonds was equal to its fair value.
Subordinated tax increment revenue bonds at cost	22,400,000
Impairment loss on investments		18,737,000	[2]	11,717,000	[2]
Subordinated bonds received on exchange of bonds	57,700,000
Investment at fair value	10,700,000	0
Investments		26,723,000
Subordinate Tax Increment Revenue Note [Member]
Fair Value Measurements [Line Items]
Impairment loss on investments				598,000	[2]
Senior Tax Increment Revenue Bonds [Member]
Fair Value Measurements [Line Items]
Investment at fair value	51,300,000
Fixed Rate Debt [Member]
Fair Value Measurements [Line Items]
Debt fair value		2,200,000,000		2,400,000,000
Variable-Rate Debt [Member]
Fair Value Measurements [Line Items]
Debt fair value		$ 561,500,000		$ 252,200,000

[1] Consolidated Variable Interest Entities' Assets and Liabilities included in the above balances (See Note 3):

[2] Total gains (losses) exclude impairments on disposed assets.