Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
ASSETS
Real estate and development in process, net		$ 17,622,212		$ 16,752,119
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,922,408		2,964,572
Other Liabilities		387,994		503,726
Total liabilities and equity / capital		21,284,905		20,256,477
Carying value of the Company's investment in unconsolidated joint ventures		955,647		956,309
Right-of-use assets - finance leases		237,394
Right of use assets - operating leases		148,640	$ 151,800
Lease liabilities - finance leases		224,042
Lease liabilities - operating leases		200,180	$ 199,300
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net	[1]	3,904,400		3,545,906
Other assets		502,706		543,512
Total assets		4,407,106		4,089,418
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,218,853		2,017,609
Other Liabilities	[2]	749,675		582,006
Members'/Partners' equity		1,438,578		1,489,803
Total liabilities and equity / capital		4,407,106		4,089,418
Company's share of equity		591,905		622,498
Basis differentials	[3]	341,318		308,721
Carying value of the Company's investment in unconsolidated joint ventures	[4]	933,223		931,219
Right-of-use assets - finance leases		383,900
Right of use assets - operating leases		12,100
Lease liabilities - finance leases		510,800
Lease liabilities - operating leases		17,300
Colorado Center [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		311,300		316,700
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		$ 22,400		$ 25,100

[1] At December 31, 2019, this amount includes right of use assets - finance leases and right of use assets - operating leases totaling approximately $383.9 million and $12.1 million, respectively.

[2] At December 31, 2019, this amount includes lease liabilities - finance leases and lease liabilities - operating leases totaling approximately $510.8 million and $17.3 million, respectively.

[3] 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, 2019 and 2018, there was an aggregate basis differential of approximately $311.3 million and $316.7 million, respectively, 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.

[4] Investments with deficit balances aggregating approximately $22.4 million and $25.1 million at December 31, 2019 and 2018, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.