Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Jun. 30, 2021		Dec. 31, 2020
ASSETS
Real estate and development in process, net		$ 18,072,453		$ 17,818,807
Total assets		22,059,076		22,858,190
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,901,709		2,909,081
Other Liabilities		370,990		412,084
Members’/Partners’ equity		5,749,342		5,996,083
Total liabilities and equity / capital		22,059,076		22,858,190
Carying value of the Company's investment in unconsolidated joint ventures		1,305,589		1,310,478
Right-of-use assets - finance leases		237,765		237,393
Right of use assets - operating leases		170,331	[1]	146,406
Lease liabilities - finance leases		243,381		236,492
Lease liabilities - operating leases		226,594		201,713
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net	[2]	4,751,881		4,708,571
Other assets		521,766		531,071
Total assets		5,273,647		5,239,642
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,715,677		2,637,911
Other Liabilities	[3]	600,402		650,433
Members’/Partners’ equity		1,957,568		1,951,298
Total liabilities and equity / capital		5,273,647		5,239,642
Company's share of equity		929,421		936,087
Basis differentials	[4]	340,681		337,832
Carying value of the Company's investment in unconsolidated joint ventures	[5]	1,270,102		1,273,919
Right-of-use assets - finance leases		248,900		248,900
Right of use assets - operating leases		22,000		22,500
Lease liabilities - finance leases		387,100		388,700
Lease liabilities - operating leases		29,400		29,000
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		35,500		36,600
Colorado Center
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		305,902		307,328
Carying value of the Company's investment in unconsolidated joint ventures	[6]	229,564		227,671
Gateway Commons Complex [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		52,104		51,875
Carying value of the Company's investment in unconsolidated joint ventures	[6]	331,389		336,206
Dock 72
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		(51,137)		(52,243)
Carying value of the Company's investment in unconsolidated joint ventures	[6]	$ 28,116		$ 29,536

[1] See Note 4.

[2] At June 30, 2021 and December 31, 2020, this amount included right of use assets - finance leases totaling approximately $248.9 million and $248.9 million, respectively, and right of use assets - operating leases totaling approximately $22.0 million and $22.5 million, respectively.

[3] At June 30, 2021 and December 31, 2020, this amount included lease liabilities - finance leases totaling approximately $387.1 million and $388.7 million, respectively, and lease liabilities - operating leases totaling approximately $29.4 million and $29.0 million, respectively.

[4] 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. The majority of the Company’s basis differences are as follows: June 30,
2021December 31,
2020Property(in thousands)Colorado Center$305,902 $307,328 Gateway Commons52,104 51,875 Dock 72(51,137)(52,243) These basis differentials (excluding land) will be amortized over the remaining lives of the related assets and liabilities.

[5] Investments with deficit balances aggregating approximately $35.5 million and $36.6 million at June 30, 2021 and December 31, 2020, respectively, are reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

[6] Investments with deficit balances aggregating approximately $35.5 million and $36.6 million at June 30, 2021 and December 31, 2020, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.