Investment in Unconsolidated Ventures Investment in Unconsolidated Ventures (Financial Position of Unconsolidated Real Estate Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Company's share of equity (Company's Basis)	$ 176,875	$ 193,555
Unconsolidated Real Estate Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Net property	813,056	923,536
Other assets	165,854	174,677
Other liabilities	27,054	53,645
Debt	709,975	724,780
Equity	241,881	319,788
Company's share of equity (Company's Basis)	$ 176,875	$ 193,555