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Investments in Unconsolidated Joint Ventures (Balance Sheets of the Unconsolidated Joint Ventures) (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
ASSETS |  |  |
Real estate and development in process, net |  | $ 16,849,143 | $ 16,507,008
Liabilities and Members'/Partners' Equity [Abstract] |  |  |
Mortgage notes payable, net |  | 2,967,548 | 2,979,281
Other Liabilities |  | 468,433 | 443,980
Total liabilities and equity / capital |  | 20,137,498 | 19,372,233
Carrying value of the Company's investments in unconsolidated joint ventures |  | 925,431 | 619,925
Unconsolidated Joint Ventures [Member] |  |  |
ASSETS |  |  |
Real estate and development in process, net |  | 3,475,909 | 1,768,996
Other assets |  | 523,177 | 367,743
Total assets |  | 3,999,086 | 2,136,739
Liabilities and Members'/Partners' Equity [Abstract] |  |  |
Mortgage notes payable, net |  | 1,975,260 | 1,437,440
Other Liabilities |  | 589,394 | 99,215
Members'/Partners' equity |  | 1,434,432 | 600,084
Total liabilities and equity / capital |  | 3,999,086 | 2,136,739
Company's share of equity |  | 593,427 | 286,495
Basis differentials | [1] | 307,981 | 307,485
Carrying value of the Company's investments in unconsolidated joint ventures | [2],[3] | 901,408 | 593,980
Unconsolidated Joint Ventures [Member] |  |  |
Liabilities and Members'/Partners' Equity [Abstract] |  |  |
Other Liabilities |  | (24,000) | (25,900)
Basis differentials |  | $ 318,200 | $ 322,500
[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 September 30, 2018 and December 31, 2017, there was an aggregate basis differential of approximately $318.2 million and $322.5 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.
[2] | Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheet
[3] | Investments with deficit balances aggregating approximately $24.0 million and $25.9 million at September 30, 2018 and December 31, 2017, respectively, have been reflected within Other Liabilities in the Company’s Consolidated Balance Sheets.

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- Definition 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. + References No definition available. + Details
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- Definition Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(d)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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