Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
ASSETS
Real estate and development in process, net		$ 17,873,023	$ 17,818,807
Total assets		22,213,552	22,858,190
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,904,672	2,909,081
Other Liabilities		399,965	412,084
Members’/Partners’ equity		5,775,641	5,996,083
Total liabilities and equity / capital		22,213,552	22,858,190
Carying value of the Company's investment in unconsolidated joint ventures		1,307,725	1,310,478
Right-of-use assets - finance leases		237,017	237,393
Right of use assets - operating leases		144,143	146,406
Lease liabilities - finance leases		239,361	236,492
Lease liabilities - operating leases		200,383	201,713
Unconsolidated Joint Ventures [Member]
ASSETS
Real estate and development in process, net	[1]	4,711,593	4,708,571
Other assets		505,554	531,071
Total assets		5,217,147	5,239,642
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Mortgage and notes payable, net		2,662,616	2,637,911
Other Liabilities	[2]	599,354	650,433
Members’/Partners’ equity		1,955,177	1,951,298
Total liabilities and equity / capital		5,217,147	5,239,642
Company's share of equity		933,739	936,087
Basis differentials	[3]	338,337	337,832
Carying value of the Company's investment in unconsolidated joint ventures	[4]	1,272,076	1,273,919
Right-of-use assets - finance leases		248,900	248,900
Right of use assets - operating leases		22,200	22,500
Lease liabilities - finance leases		387,900	388,700
Lease liabilities - operating leases		29,200	29,000
Unconsolidated Joint Ventures [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Other Liabilities		35,600	36,600
Colorado Center
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		306,903	307,328
Carying value of the Company's investment in unconsolidated joint ventures	[5]	229,094	227,671
Gateway Commons Complex [Member]
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		50,682	51,875
Carying value of the Company's investment in unconsolidated joint ventures	[5]	332,591	336,206
Dock 72
LIABILITIES AND MEMBERS'/PARTNERS' EQUITY
Basis differentials		(51,708)	(52,243)
Carying value of the Company's investment in unconsolidated joint ventures	[5]	$ 27,936	$ 29,536

[1] At March 31, 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 $22.2 million and $22.5 million, respectively.

[2] At March 31, 2021 and December 31, 2020, this amount included lease liabilities - finance leases totaling approximately $387.9 million and $388.7 million, respectively, and lease liabilities - operating leases totaling approximately $29.2 million and $29.0 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. The Company’s basis differences are as follows: March 31,
2021December 31,
2020 (in thousands)PropertyColorado Center$306,903 $307,328 Gateway Commons50,682 51,875 Dock 72(51,708)(52,243) These basis differentials (excluding land) will be amortized over the remaining lives of the related assets and liabilities.

[4] Investments with deficit balances aggregating approximately $35.6 million and $36.6 million at March 31, 2021 and December 31, 2020, respectively, are reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

[5] Investments with deficit balances aggregating approximately $35.6 million and $36.6 million at March 31, 2021 and December 31, 2020, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.