Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Real estate and development in process, net	$ 15,886,276		$ 15,817,194
Mortgage and notes payable	4,328,464		4,449,734
Other liabilities	517,428		578,969
Total liabilities and equity	18,875,160		20,162,251
Carrying value of the Company's investments in unconsolidated joint ventures	180,149		126,084
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Real estate and development in process, net	1,014,663		924,297
Other assets	182,905		163,149
Total assets	1,197,568		1,087,446
Mortgage and notes payable	753,692		749,732
Other liabilities	23,180		28,830
Members'/Partners' equity	420,696		308,884
Total liabilities and equity	1,197,568		1,087,446
Company's share of equity	208,125		154,726
Basis differentials	(27,976)	[1]	(28,642)	[1]
Carrying value of the Company's investments in unconsolidated joint ventures	$ 180,149		$ 126,084

[1] This amount represents the aggregate difference between the Company’s historical cost basis and the basis reflected at the joint venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from impairment of investments and upon the transfer of assets that were previously owned by the Company into a joint venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the joint venture level.