Fair Value Measurements Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) (USD $)									6 Months Ended		12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended							6 Months Ended				6 Months Ended
	Jun. 30, 2012 Impaired Property [Member]		Dec. 31, 2011 Impaired Property [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member]		Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Discounted Cash Flows [Member] Y		Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Minimum [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Minimum [Member] Discounted Cash Flows [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Maximum [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Impaired Property [Member] Maximum [Member] Discounted Cash Flows [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Notes Receivable From Real Estate Joint Ventures And Partnerships [Member] Discounted Cash Flows [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Tax Increment Revenue Bonds [Member] Discounted Cash Flows [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Tax Increment Revenue Bonds [Member] Minimum [Member] Discounted Cash Flows [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Tax Increment Revenue Bonds [Member] Maximum [Member] Discounted Cash Flows [Member]	Jun. 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]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Fixed-Rate Debt [Member] Minimum [Member] Discounted Cash Flows [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Fixed-Rate Debt [Member] Maximum [Member] Discounted Cash Flows [Member]	Jun. 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]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Variable-Rate Debt [Member] Minimum [Member] Discounted Cash Flows [Member]	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Variable-Rate Debt [Member] Maximum [Member] Discounted Cash Flows [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Property	$ 46,375,000	[1]	$ 98,596,000			$ 46,375,000	[1]	$ 98,207,000
Notes receivable from real estae joint ventures and partnerships fari value				91,177,000	153,532,000
Investments				26,505,000	26,505,000
Debt fair value																			1,958,305,000	2,054,670,000			388,486,000	531,353,000
Assumption For Fair Value Discount Rate											8.00%	9.50%	13.00%	10.00%	2.80%	7.50%					1.00%	6.40%			1.40%	5.00%
Assumption For Fair Value Market Capitalization Rate												9.00%		10.50%
Assumption For Fair Value Holding Period (Years)									1
Assumption For Fair Value Expected Future Growth Rate																	1.00%	4.00%
Assumption For Fair Value Expected Inflation Rate									3.00%	[2]							1.00%	2.00%
Assumption For Fair Value Market Rent Growth Rate									3.00%	[2]
Assumption For Fair Value Expense Growth Rate									3.00%	[2]
Assumption For Fair Value Vacancy Rate									5.00%	[2]
Assumption For Fair Value Renewal Rate									75.00%	[2]
Assumption For Fair Value Market Rent Rate									10.52	[2]
Assumption For Fair Value Leasing Costs Per Square Foot									$ 16.50	[2]

[1] In accordance with our policy of evaluating and recording impairments on the disposal of long-lived assets, property with a carrying amount of $50.7 million was written down to a fair value of $46.4 million, resulting in a loss of $4.3 million, which was included in earnings for the 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] Only applies to one property valuation.