Investment in Unconsolidated Ventures (Financial Position of Unconsolidated Real Estate Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Financial position of the Real Estate Ventures
Debt	$ (745,830)
Company's share of equity (Company's basis)	115,807	84,372
Unconsolidated real estate ventures [Member]
Financial position of the Real Estate Ventures
Net property	(846,643)	(804,705)
Other Assets	(110,520)	(105,576)
Other Liabilities	(48,798)	(44,509)
Debt	(745,830)	(748,387)
Equity	162,535	117,385
Company's share of equity (Company's basis)	$ 115,807	$ 84,372

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