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(Common Units) (Narrative) (Details) $ / shares in Units, $ in Millions |  | 9 Months Ended
--- | --- | ---
Feb. 04, 2018 USD ($) shares | Sep. 30, 2018 USD ($) shares yr $ / shares
OP Units [Member] |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |
OP Units for redemption (in shares) |  | 61,021
Redemption of OP units issued on conversion of LTIP Units (in shares) |  | 47,985
Restriction on redemption of OP Unit to Common Stock (in years) | yr |  | 1
Redemption of OP Unit equivalent to Common Stock (in shares) |  | 1
Common units of operating partnership if converted value | $ |  | $ 2,200.0
Closing price of common stock (in dollars per share) | $ / shares |  | $ 123.09
2015 MYLTIP [Member] |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |
Final awards percentage of target | 22.00% |
Value of MYLTIP Awards | $ | $ 3.6 |
2015 MYLTIP Units Forfeited | 337,847 |
Boston Properties Limited Partnership | OP Units [Member] |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |
MYLTIP distribution prior to measurement date |  | 10.00%
Boston Properties Limited Partnership | 2016 MYLTIP [Member] |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |
2016 MYLTIPs (in units) |  | 471,579
Boston Properties Limited Partnership | 2017 MYLTIP [Member] |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |
2017 MYLTIP (in units) |  | 398,871
Boston Properties Limited Partnership | 2018 MYLTIP [Member] |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |
2018 MYLTIP |  | 341,366

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