Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
ASSETS
Real estate and development in process, net		$ 15,740,152	$ 15,555,641
Liabilities and Members'/Partners' Equity [Abstract]
Mortgage notes payable, net		3,189,013	3,435,242
Other Liabilities		508,952	483,601
Total liabilities and equity / capital		18,963,965	18,351,486
Carrying value of the Company's investments in unconsolidated joint ventures		252,618	235,224
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net		1,124,267	1,072,412
Other assets		237,196	252,285
Total assets		1,361,463	1,324,697
Liabilities and Members'/Partners' Equity [Abstract]
Mortgage notes payable, net		827,987	830,125
Other Liabilities		47,685	44,549
Members'/Partners' equity		485,791	450,023
Total liabilities and equity / capital		1,361,463	1,324,697
Company's share of equity		255,362	237,070
Basis differentials	[1]	(26,673)	(27,047)
Carrying value of the Company's investments in unconsolidated joint ventures	[2],[3]	228,689	210,023
Unconsolidated Joint Ventures [Member]
Liabilities and Members'/Partners' Equity [Abstract]
Carrying value of the Company's investments in unconsolidated joint ventures		$ (23,900)	$ (25,200)

[1] (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.

[2] Investments with deficit balances aggregating approximately $23.9 million and $25.2 million at June 30, 2016 and December 31, 2015, respectively, have been reflected within Other Liabilities on the Company’s Consolidated Balance Sheets.

[3] Investments with deficit balances aggregating approximately $23.9 million and $25.2 million at June 30, 2016 and December 31, 2015, respectively, have been reflected within Other Liabilities on the Company’s Consolidated Balance Sheets.