Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
ASSETS
Real estate and development in process, net		$ 15,925,028	$ 15,555,641
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,063,087	3,435,242
Other Liabilities		450,821	483,601
Total liabilities and equity / capital		18,851,643	18,351,486
Carying value of the Company's investment in unconsolidated joint ventures		775,198	235,224
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net		1,519,217	1,072,412
Other assets		297,263	252,285
Total assets		1,816,480	1,324,697
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		865,665	830,125
Other Liabilities		67,167	44,549
Members'/Partners' equity		883,648	450,023
Total liabilities and equity / capital		1,816,480	1,324,697
Company's share of equity		450,662	237,070
Basis differentials	[1]	302,449	(27,047)
Carying value of the Company's investment in unconsolidated joint ventures	[2]	753,111	210,023
Colorado Center [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		328,800
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		$ 22,100	$ 25,200

[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 result from impairments of investments, acquisitions through joint ventures with no change in control 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. At December 31, 2016, there is an aggregate basis differential of approximately $328.8 million between the carrying value of the Company’s investment in the joint venture that owns Colorado Center and the joint venture’s basis in the assets and liabilities, which differential (excluding land) shall be amortized over the remaining lives of the related assets and liabilities.

[2] Investments with deficit balances aggregating approximately $22.1 million and $25.2 million at December 31, 2016 and 2015, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.