Fair Value Measurements Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) (USD $)																			12 Months Ended						9 Months Ended
	Sep. 30, 2012 Impaired Property [Member]		Dec. 31, 2011 Impaired Property [Member]		Sep. 30, 2012 Impaired Property Held For Sale [Member]		Dec. 31, 2011 Impaired Property Held For Sale [Member]		Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Fixed-Rate Debt [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Fixed-Rate Debt [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Variable-Rate Debt [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Variable-Rate Debt [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member]		Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member]		Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Minimum [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Maximum [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property Held For Sale [Member]		Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Impaired Property Held For Sale [Member]		Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Fixed-Rate Debt [Member] Minimum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Fixed-Rate Debt [Member] Maximum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Variable-Rate Debt [Member] Minimum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Variable-Rate Debt [Member] Maximum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Notes Receivable From Real Estate Joint Ventures And Partnerships [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Tax Increment Revenue Bonds [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Tax Increment Revenue Bonds [Member] Minimum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Tax Increment Revenue Bonds [Member] Maximum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Impaired Property [Member] Y		Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Impaired Property [Member] Minimum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Impaired Property [Member] Maximum [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Discounted Cash Flows [Member] Impaired Property Held For Sale [Member] Y
Fair Value Inputs, Quantitative Information [Line Items]
Property	$ 13,906,000	[1]	$ 98,596,000	[2]											$ 13,906,000	[1]	$ 98,207,000	[2]
Property held for sale					49,806,000	[3]	45,157,000	[4]													1,500,000	[4]	10,675,000	[3]
Notes receivable from real estae joint ventures and partnerships fair value									93,257,000	153,532,000
Investments									26,505,000	26,505,000
Debt fair value											1,967,343,000	2,054,670,000	409,952,000	531,353,000
Assumption For Fair Value Discount Rate																			8.00%	13.00%	10.00%				1.20%	6.00%	1.40%	5.00%	3.20%	7.50%			10.00%				9.80%
Assumption For Fair Value Market Capitalization Rate																																			9.30%	9.50%	10.50%
Assumption For Fair Value Holding Period (Years)																																	1				1
Assumption For Fair Value Expected Future Growth Rate																															1.00%	4.00%
Assumption For Fair Value Expected Inflation Rate																															1.00%	2.00%	3.00%	[5]
Assumption For Fair Value Market Rent Growth Rate																																	3.00%	[5]
Assumption For Fair Value Expense Growth Rate																																	3.00%	[5]
Assumption For Fair Value Vacancy Rate																																	5.00%	[5]
Assumption For Fair Value Renewal Rate																																	75.00%	[5]
Assumption For Fair Value Market Rent Rate																																	10.52	[5]
Assumption For Fair Value Leasing Costs Per Square Foot																																	$ 16.50	[5]

[1] In accordance with our policy of evaluating and recording impairments on the disposal of long-lived assets, property with a carrying amount of $16.8 million was written down to a fair value of $13.9 million, resulting in a loss of $2.9 million, which was included in earnings for the nine month period. Management’s estimate of the fair value of these properties was determined using Level 3 inputs. See the quantitative information about the significant unobservable inputs used for our Level 3 fair value measurements table below.

[2] In accordance with our policy of evaluating and recording impairments on the disposal of long-lived assets, property with a carrying amount of $135.5 million was written down to a fair value of $98.6 million, resulting in a loss of $36.9 million, which was included in earnings for the twelve month period. Management’s estimate of the fair value of these properties was determined using the expected sales price of an executed agreement for the Level 2 input and using third party broker valuations, bona fide purchase offers, cash flow models and discount rates ranging from 8% to 13% for the Level 3 inputs.

[3] Property held for sale with a carrying amount of $53.8 million was written down to a fair value of $49.8 million less costs to sell of $0.8 million, resulting in a loss of $4.8 million, which was included in discontinued operations in the Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) for the nine month period. Management’s estimate of the fair value of these properties was determined using bona fide purchase offers for the Level 2 inputs, and see the quantitative information about the significant unobservable inputs used for our Level 3 fair value measurements table below.

[4] Property held for sale with a carrying amount of $57.0 million was written down to a fair value of $45.2 million less costs to sell of $2.0 million, resulting in a loss of $13.8 million, which was included in discontinued operations in the Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) for the twelve month period. Management’s estimate of the fair value of these properties was determined using the expected sales price of executed agreements for the Level 2 inputs and a cash flow model using a discount rate of 10% for the Level 3 input.

[5] Only applies to one property valuation.