Investment in Unconsolidated Ventures (Financial Position of Unconsolidated Real Estate Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Austin, Texas [Member]	Sep. 30, 2014 Unconsolidated Real Estate Ventures [Member]		Dec. 31, 2013 Unconsolidated Real Estate Ventures [Member]		Jul. 31, 2014 Crossings at Lakeline [Member]
Schedule of Equity Method Investments [Line Items]
Net property				$ 1,140,798		$ 965,475
Other assets				166,020		164,152
Other liabilities				59,690		49,442
Debt				852,636		699,860		34,500
Equity				394,492		380,325
Company's share of equity (Company's Basis)	$ 197,539	$ 180,512	$ (1,200)	$ 197,539	[1]	$ 180,512	[1]

[1] (a) 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.