Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Real estate and development in process, net	$ 15,860,776		$ 15,817,194
Mortgage and notes payable	4,430,110		4,449,734
Other liabilities	556,772		578,969
Total liabilities and equity	18,979,568		20,162,251
Carrying value of the Company's investments in unconsolidated joint ventures	127,356		126,084
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Real estate and development in process, net	921,524		924,297
Other assets	158,375		163,149
Total assets	1,079,899		1,087,446
Mortgage and notes payable	748,700		749,732
Other liabilities	19,593		28,830
Members'/Partners' equity	311,606		308,884
Total liabilities and equity	1,079,899		1,087,446
Company's share of equity	155,807		154,726
Basis differentials	(28,451)	[1]	(28,642)	[1]
Carrying value of the Company's investments in unconsolidated joint ventures	$ 127,356		$ 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.