Basis of Presentation and Significant Accounting Policies (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2009
Property Plant And Equipment Net By Type Abstract
Property Plant And Equipment Useful Life Minimum									7
Property Plant And Equipment Useful Life Maximum									40
Interest Costs Capitalized									$ 1,197,000	$ 864,000
Property Plant And Equipment [Line Items]
Tenant buy-outs, impairment losses and other acquisition related costs									58,299,000	129,458,000	73,763,000
Identified Intangibles
Identified Intangible Assets, Net	319,704,000				346,157,000				319,704,000	346,157,000
Identified Intangible Liabilities (included in deferred credit)	467,187,000				521,372,000				467,187,000	521,372,000
Significant Policies Other Details [Abstract]
Mezzanine Loan Loss Accural Reversal									(72,270,000)	(53,100,000)	190,738,000
Accounts receivable, allowance for doubtful accounts	43,241,000				62,979,000				43,241,000	62,979,000
Receivables Arising From Straight Lining Of Rents Allowance	4,046,000				7,316,000				4,046,000	7,316,000
Condominium Assets held for sale	60,785,000				84,397,000				60,785,000	84,397,000
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	100.00%				100.00%				100.00%	100.00%	100.00%
Minimum Percentage of Taxable Income Distributed As Dividends	90.00%								90.00%
Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
NET INCOME attributable to common shareholders	69,508,000	41,135,000	91,913,000	399,215,000	243,414,000	95,192,000	57,840,000	200,285,000	601,771,000	596,731,000	49,093,000
Depreciation and Amortization									225,802,000	216,473,000	247,023,000
Mezzanine Loans Receivable									(82,512,000)	(104,727,000)	171,380,000
Straight-line Rent Adjustment									(38,800,000)	(70,606,000)	(83,959,000)
Earnings of Partially Owned Entities									(96,178,000)	(62,315,000)	(82,382,000)
Stock Options									(27,697,000)	(48,399,000)	(32,643,000)
Sale of Real Estate									(18,766,000)	12,899,000	3,923,000
Derivatives									(12,160,000)	(121,120,000)	0
Other Adjustments									(6,223,000)	48,915,000	81,936,000
Estimated Taxable Income Net									545,237,000	467,851,000	354,371,000
Income Tax Liability Relating to Taxable REIT Subsidiaries Current	26,645,000				24,858,000				26,645,000	24,858,000
Explanation Differences Between Book And Tax Basis									The net basis of our assets and liabilities for tax reporting purposes is approximately $3.6 billion lower than its amount reported in our consolidated financial statements
Net Basis Difference Of Assets And Liabilities Between Tax Basis And GAAP Basis	3,600,000,000								3,600,000,000
Ordinary Income [Member]
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	93.20%				95.90%				93.20%	95.90%	63.90%
Long Term Capital Gain [Member]
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	6.80%				2.80%				6.80%	2.80%	0.90%
Return Of Capital [Member]
Tax Treatment Of Dividend [Line Items]
Percent of dividend paid to Shareholders	0.00%				1.30%				0.00%	1.30%	35.20%
Equity Method Investments [Member]
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net By Investment Category [Line Items]
Impairment Of Investments net									13,794,000	11,481,000	17,820,000
Real Estate [Member]
Property Plant And Equipment [Line Items]
Tenant buy-outs, impairment losses and other acquisition related costs									23,000,000	92,500,000	4,789,000
Cost Of Real Estate Acquisitions Not Consummated [Member]
Property Plant And Equipment [Line Items]
Tenant buy-outs, impairment losses and other acquisition related costs									32,259,000	6,945,000	0
Development Related Real Estate [Member]
Property Plant And Equipment [Line Items]
Tenant buy-outs, impairment losses and other acquisition related costs									3,040,000	0	55,307,000
Condominium Units [Member]
Property Plant And Equipment [Line Items]
Tenant buy-outs, impairment losses and other acquisition related costs									$ 0	$ 30,013,000	$ 13,667,000