Fair Value Measurements (Quantitative Information About Significant Unobservable Inputs (Level 3) Used) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Impaired Property [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Property		19,679,000	[1]
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notes receivable from real estate joint ventures and partnerships	92,719,000	93,572,000
Tax increment revenue bonds	25,850,000	26,505,000
Significant Unobservable Inputs (Level 3) [Member] | Fixed Rate Debt [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt	2,294,471,000	2,094,122,000
Significant Unobservable Inputs (Level 3) [Member] | Variable Rate Debt [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt	155,250,000	223,759,000
Significant Unobservable Inputs (Level 3) [Member] | Impaired Property [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Property	0	13,906,000	[1]
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Fixed Rate Debt [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate	1.50%	1.10%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Fixed Rate Debt [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate	6.00%	6.50%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Variable Rate Debt [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate	2.40%	1.40%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Variable Rate Debt [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate	5.00%	5.00%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Notes Receivable From Real Estate Joint Ventures And Partnerships [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate	2.70%	3.00%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Tax Increment Revenue Bonds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate	7.50%	7.50%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Tax Increment Revenue Bonds [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Expected Future Inflation Rate	1.00%	1.00%
Fair Value Input, Expected Future Growth Rate	1.00%	1.00%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Tax Increment Revenue Bonds [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Expected Future Inflation Rate	2.00%	2.00%
Fair Value Input, Expected Future Growth Rate	2.00%	4.00%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Impaired Property [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Discount Rate		10.00%
Fair Value Input, Holding Period (Years)		1 year
Fair Value Input, Expected Future Inflation Rate		3.00%	[2]
Fair Value Input, Market Rent Growth Rate		3.00%	[2]
Fair Value Input, Expense Growth Rate		3.00%	[2]
Fair Value Input, Vacancy Rate		5.00%	[2]
Fair Value Input, Renewal Rate		75.00%	[2]
Fair Value Input, Market Rent Rate		10.52	[2]
Fair Value Input, Leasing Costs Per Square Foot		16.50	[2]
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Impaired Property [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Market Capitalization Rate		9.30%
Significant Unobservable Inputs (Level 3) [Member] | Discounted Cash Flows [Member] | Impaired Property [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input, Market Capitalization Rate		9.50%

[1] In accordance with our policy of evaluating and recording impairments on the disposal of long-lived assets, property with a carrying amount of $22.4 million was written down to a fair value of $19.7 million less costs to sell of $.3 million, resulting in a loss of $3.0 million, which was included in earnings for the period. Management’s estimate of fair value of these properties was determined using a bona fide purchase offer for the Level 2 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.