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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