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Mortgage Notes Payable, Net, Mezzanine Notes Payable and Outside Members’ Notes Payable (Narrative) (Details) $ in Thousands |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 07, 2017 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2008 USD ($) | Jun. 06, 2017 USD ($) | Apr. 24, 2017 USD ($)
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Mortgage notes payable, net (amounts related to VIEs of $2,939,183 and $2,018,483 at December 31, 2017 and 2016, respectively) |  | $ 2,979,281 | $ 2,063,087 |  |  |  |
Proceeds from Issuance of Secured Debt |  | 2,300,000 | 0 | $ 0 |  |  |
Repayments of Secured Debt |  | 1,317,653 | 1,326,865 | 54,801 |  |  |
Repayments of Subordinated Debt |  | 306,000 | 0 | 0 |  |  |
Other Notes Payable |  | 0 | 180,000 |  |  |  |
Interest Payable |  | 83,646 | 243,933 |  |  |  |
Gains (losses) from early extinguishments of debt |  | $ 496 | $ (371) | (22,040) |  |  |
Number Of Mortgage Loans Accounted For Fair Value |  | 0 | 1 |  |  |  |
Mortgage Loans Accounted For At Fair Value Upon Assumption |  |  | $ 1,300,000 |  |  |  |
Interest Expense Decrease Due To Recording Mortgage Loans At Fair Value |  | $ 19,600 | 46,400 | $ 55,000 |  |  |
Cumulative Liability Related to the Fair Value of Debt Adjustment |  |  | $ 33,800 |  |  |  |
Minimum [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Coupon/Stated Rate |  | 3.43% | 4.75% |  |  |  |
Number Real Estate Assets Used For Mortgage Loan Collateral |  | 1 |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Coupon/Stated Rate |  | 7.69% | 7.69% |  |  |  |
Fixed Rate Mortgages [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Mortgage notes payable, net (amounts related to VIEs of $2,939,183 and $2,018,483 at December 31, 2017 and 2016, respectively) |  | $ 3,000,000 | $ 2,100,000 |  |  |  |
Debt, Weighted Average Interest Rate |  | 3.78% | 5.59% |  |  |  |
Variable Rate Mortgages [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Number of variable rate mortgage loans |  | 0 | 0 |  |  |  |
767 Fifth Avenue (the general motors building) [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Gains (losses) from early extinguishments of debt | $ 14,600 |  |  |  |  |  |
767 Fifth Avenue (the general motors building) [Member] | Notes Payable, Other Payables [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Repayment of a portion of members loans accrued interest and principal balance | 176,100 |  |  |  |  |  |
767 Fifth Avenue (the general motors building) [Member] | Secured Debt [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Mortgage notes payable, net (amounts related to VIEs of $2,939,183 and $2,018,483 at December 31, 2017 and 2016, respectively) |  |  |  |  |  |  | $ 2,300,000
Coupon/Stated Rate |  |  |  |  |  |  | 3.43%
Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity | $ 273,900 |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] | Junior Subordinated Debt [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Coupon/Stated Rate | 6.02% |  |  |  |  |  |
Other Long-term Debt | $ 294,000 |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] | Notes Payable, Other Payables [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Coupon/Stated Rate | 11.00% |  |  |  |  |  |
Other Notes Payable | $ 450,000 |  |  |  |  |  |
Interest Payable | $ 425,000 |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] | Secured Debt [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Ownership Percentage by Parent | 60.00% |  |  |  |  |  |
Proceeds from Issuance of Secured Debt | $ 2,300,000 |  |  |  |  |  |
Coupon/Stated Rate | 3.43% |  |  |  |  | 5.95% |
Repayments of Secured Debt | $ 1,300,000 |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] | Subordinated Debt [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Coupon/Stated Rate | 6.02% |  |  |  |  |  |
Repayments of Subordinated Debt | $ 306,000 |  |  |  |  |  |
Consolidated Properties [Member] | 767 Fifth Avenue (the general motors building) [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity |  |  |  |  |  | $ 273,900 |
Ownership Percentage by Parent |  |  |  |  |  | 60.00% |
Consolidation, Eliminations [Member] | 767 Fifth Avenue (the general motors building) [Member] | Junior Subordinated Debt [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Repayments of Other Long-term Debt |  |  |  |  | $ 263,100 |  |
Consolidation, Eliminations [Member] | Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity | 164,400 |  |  |  |  |  |
Consolidation, Eliminations [Member] | Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] | Notes Payable, Other Payables [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Other Notes Payable | 270,000 |  |  |  |  |  |
Interest Payable | 255,000 |  |  |  |  |  |
Consolidation, Eliminations [Member] | Consolidated Properties [Member] | 767 Fifth Avenue (the general motors building) [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity |  |  |  |  |  | $ 164,400 |
Boston Properties, Inc. [Member] | Consolidated Entities [Member] | 767 Fifth Avenue (the general motors building) [Member] | Notes Payable, Other Payables [Member] |  |  |  |  |  |  |
Mortgage Notes Payable [Line Items] |  |  |  |  |  |  |
Other Notes Payable | 180,000 |  |  |  |  |  |
Interest Payable | $ 170,000 |  |  |  |  |  |

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