Fair Value Measurements (Assets Measured On Nonrecurring Basis) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 43,910,000		$ 0
Total Gains (Losses)	(9,579,000)	[1]
Property, net	3,359,011,000	[2]	3,330,004,000	[2]
Investment in Real Estate Joint Ventures and Partnerships, net	289,049,000		285,666,000
Impaired Property [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property	19,679,000	[3]
Total Gains (Losses)	(2,971,000)	[1],[3]
Property, net	22,400,000
Cost to sell property	300,000
Impaired Investment In Real Estate Joint Ventures And Partnerships [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in real estate joint ventures and partnerships	24,231,000	[4]
Total Gains (Losses)	(6,608,000)	[1],[4]
Investment in Real Estate Joint Ventures and Partnerships, net	30,800,000
Quoted Prices In Active Markets For Identical Assets And Liabilities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	30,004,000
Significant Other Observable Inputs (Level 2) [Member] | Impaired Property [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property	5,773,000	[3]
Significant Other Observable Inputs (Level 2) [Member] | Impaired Investment In Real Estate Joint Ventures And Partnerships [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in real estate joint ventures and partnerships	24,231,000	[4]
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	13,906,000
Significant Unobservable Inputs (Level 3) [Member] | Impaired Property [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property	$ 13,906,000	[3]	$ 0

[1] Total gains (losses) are reflected throughout 2012 and exclude impairments on disposed assets because they are no longer held by us.

[2] Consolidated Variable Interest Entities’ Assets and Liabilities included in the above balances (See Note 17):

[3] 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.

[4] Our net investment in real estate joint ventures and partnerships with a carrying amount of $30.8 million was written down to a fair value of $24.2 million, resulting in a loss of $6.6 million, which was included in earnings for the period. Management’s estimate of fair value of this investment was determined using the weighted average of the bona fide purchase offers received for the Level 2 inputs.