Investment in Unconsolidated Ventures (Financial Position of Unconsolidated Real Estate Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)	$ 233,478		$ 225,004
Unconsolidated Real Estate Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Net property	1,294,503		1,281,282
Other assets	180,803		195,121
Other liabilities	59,829		68,481
Debt	969,322		965,077
Equity	446,155		442,845
Company's share of equity (Company's basis)	$ 233,478	[1],[2]	$ 225,004	[1],[2]

[1] This amount includes the effect of the basis difference between the Company's historical cost basis and the basis recorded at the Real Estate Venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from the impairment of investments, purchases of third party interests in existing Real Estate Ventures and upon the transfer of assets that were previously owned by the Company into a Real Estate Venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the Real Estate Venture level.

[2] Does not include the negative investment balance of one real estate venture totaling $1.2 million as of March 31, 2015 and December 31, 2014, respectively, which is included in other liabilities.