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Noncontrolling Interests (Property Partnerships) (Narrative) (Details) - USD ($) $ in Thousands |  | 12 Months Ended |
--- | --- | --- | ---
May 12, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jun. 06, 2017
Noncontrolling Interest [Line Items] |  |  |  |  |
Property partnerships |  | $ 1,711,445 | $ 1,683,760 |  |
Proceeds from sales of real estate |  | 455,409 | 29,810 | $ 122,750 |
Gains on sales of real estate |  | 182,356 | 7,663 | 80,606 |
Boston Properties Limited Partnership |  |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |  |
Proceeds from sales of real estate |  | 455,409 | 29,810 | 122,750 |
Gains on sales of real estate |  | 190,716 | $ 8,240 | $ 82,775 |
Salesforce Tower | Consolidated Properties [Member] |  |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |  |
Ownership Percentage | 5.00% |  |  |  |
Portion of project costs covered by a construction loan | 50.00% |  |  |  |
Portion of costs funded (in percentage) | 50.00% |  |  |  |
Debt Instrument, Basis Spread on Variable Rate | 3.00% |  |  |  |
Salesforce Tower | Boston Properties, Inc. [Member] | Consolidated Properties [Member] |  |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |  |
Costs funded (in percentage) | 2.50% |  |  |  |
Preferred equity funded |  | $ 22,600 |  |  |
767 Fifth Avenue (the general motors building) [Member] | Consolidated Properties [Member] |  |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |  |
Ownership Percentage by Parent |  |  |  |  | 60.00%
Unpaid principal balance of the members' notes payable contributed to equity |  |  |  |  | $ 273,900
Property partnerships |  |  |  |  | 109,600
Consolidation, Eliminations [Member] | 767 Fifth Avenue (the general motors building) [Member] | Consolidated Properties [Member] |  |  |  |  |
Noncontrolling Interest [Line Items] |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity |  |  |  |  | $ 164,400

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