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(Common Units) (Narrative) (Details) $ / shares in Units, $ in Millions |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Feb. 04, 2018 USD ($) shares | Feb. 03, 2017 USD ($) shares | Feb. 04, 2016 USD ($) shares | Dec. 31, 2018 USD ($) shares yr $ / shares | Dec. 31, 2017 shares | May 02, 2016 shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Conversion of LTIP Units to OP Units (in units) |  |  |  |  |  | 625,043
MYLTIP 2014 |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Final awards percentage of target |  | 27.70% |  |  |  |
Value of MYLTIP Awards | $ |  | $ 3.5 |  |  |  |
MYLTIP Units forfeited |  | 447,386 |  |  |  |
2012 OPP and 2013 MYLTIP [Member] |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Conversion of LTIP Units to OP Units (in units) |  |  |  |  |  | 32,349
OP Units [Member] |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
OP Units for redemption (in shares) |  |  |  | 83,136 | 495,637 |
Redemption of OP units issued on conversion of LTIP Units (in shares) |  |  |  | 48,389 | 36,486 |
MYLTIP Units distribution as percentage of OP Unit distribution prior to measurement date |  |  |  | 10.00% |  |
Restriction on redemption of OP Unit to Common Stock (in years) | yr |  |  |  | 1 |  |
Redemption of OP Unit equivalence to Common Stock (in shares) |  |  |  | 1 |  |
Common units of operating partnership if converted value | $ |  |  |  | $ 2,000.0 |  |
Closing price of common stock (in dollars per share) | $ / shares |  |  |  | $ 112.55 |  |
MYLTIP 2015 [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 |  |  |  |  |
MYLTIP Units forfeited | 337,847 |  |  |  |  |
MYLTIP 2013 |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
Final awards percentage of target |  |  | 109.50% |  |  |
Value of MYLTIP Awards | $ |  |  | $ 13.5 |  |  |
MYLTIP Units forfeited |  |  | 205,762 |  |  |
Boston Properties Limited Partnership | MYLTIP 2014 |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
2014 MYLTIP |  |  |  | 23,187 |  |
Boston Properties Limited Partnership | MYLTIP 2016 [Member] |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
2016 MYLTIP |  |  |  | 471,579 |  |
Boston Properties Limited Partnership | MYLTIP 2017 [Member] |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
2017 MYLTIP |  |  |  | 398,871 |  |
Boston Properties Limited Partnership | MYLTIP 2015 [Member] |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
2015 MYLTIP |  |  |  | 28,724 |  |
Boston Properties Limited Partnership | MYLTIP 2018 |  |  |  |  |  |
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] |  |  |  |  |  |
2018 MYLTIP |  |  |  | 341,366 |  |

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