Investment in Unconsolidated Ventures (Financial Position of Unconsolidated Real Estate Ventures) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Loss on real estate venture formation	$ 950	$ 0	$ 950	$ 0
Financial position of the Real Estate Ventures
Company's share of equity (Company's basis)	179,037		179,037		115,807
Unconsolidated real estate ventures [Member]
Financial position of the Real Estate Ventures
Net property	925,227		925,227		846,643
Other Assets	180,957		180,957		110,520
Other Liabilities	55,592		55,592		48,798
Debt	740,885		740,885		745,830
Equity	309,707		309,707		162,535
Company's share of equity (Company's basis)	$ 179,037		$ 179,037		$ 115,807