Investment in Unconsolidated Ventures Investment in Unconsolidated Ventures (Financial Position of Unconsolidated Real Estate Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Company's share of equity (Company's Basis)	$ 184,802	$ 193,555
Unconsolidated Real Estate Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Net property	823,199	923,536
Other assets	168,077	174,677
Other liabilities	31,209	53,645
Debt	726,507	724,780
Equity	233,560	319,788
Company's share of equity (Company's Basis)	$ 184,802	$ 193,555