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Unsecured Senior Notes (Narrative) (Details) - USD ($)
$ in Thousands
9 Months Ended
May 05, 2020
Sep. 30, 2020
Sep. 30, 2019
Debt Instrument [Line Items]      
Proceeds from unsecured senior notes   $ 1,248,125 $ 1,548,106
Boston Properties Limited Partnership      
Debt Instrument [Line Items]      
Proceeds from unsecured senior notes   $ 1,248,125 $ 1,548,106
Debt Instrument, Covenant Description   The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60%, (2) a secured debt leverage ratio not to exceed 50%, (3) an interest coverage ratio of greater than 1.50, and (4) an unencumbered asset value of not less than 150% of unsecured debt.  
Debt Instrument, Covenant Compliance   At September 30, 2020, Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements.  
Senior Notes | Boston Properties Limited Partnership      
Debt Instrument [Line Items]      
Debt   $ 9,700,000  
3.343 % unsecured senior notes [Member] | Senior Notes | Boston Properties Limited Partnership      
Debt Instrument [Line Items]      
Debt $ 1,250,000 $ 1,250,000  
Debt Instrument, Interest Rate, Stated Percentage 3.25% 3.25%  
Senior Notes Pricing 99.85%    
Debt Instrument, Interest Rate, Effective Percentage 3.343% 3.343% [1]  
Proceeds from unsecured senior notes $ 1,240,000    
[1] Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.