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Basis Of Presentation And Summary Of Significant Accounting Policies Narrative (Details)
$ in Thousands
 3 Months Ended
Sep. 30, 2019
USD ($)
Dec. 31, 2018
USD ($)
Schedule of Equity Method Investments [Line Items]    
Number of VIEs that are consolidated 6  
Redeemable deferred stock units—54,610 units outstanding at redemption value at September 30, 2019 $ 7,081 $ 0
Accounts payable and accrued expenses $ 421,269 276,645
In-service Properties [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of VIEs that are consolidated 5  
Boston Properties Limited Partnership    
Schedule of Equity Method Investments [Line Items]    
Redeemable deferred stock units—54,610 units outstanding at redemption value at September 30, 2019 $ 7,081 0
Accounts payable and accrued expenses 421,269 $ 276,645
Deferred Compensation for Directors [Member]    
Schedule of Equity Method Investments [Line Items]    
Change in classification of director deferred compensation plan 7,900  
Redeemable deferred stock units—54,610 units outstanding at redemption value at September 30, 2019 7,300  
Accounts payable and accrued expenses 600  
Deferred Compensation for Directors [Member] | Boston Properties Limited Partnership    
Schedule of Equity Method Investments [Line Items]    
Change in classification of director deferred compensation plan 7,900  
Redeemable deferred stock units—54,610 units outstanding at redemption value at September 30, 2019 7,300  
Accounts payable and accrued expenses $ 600