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Unsecured Senior Notes Unsecured Senior Notes (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 17, 2017
Dec. 04, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]          
Loss on Extinguishment of Debt     $ (496) $ 371 $ 22,040
Repayments of Unsecured Debt     848,020 0 0
Proceeds from unsecured senior notes     $ 847,935 1,989,790 0
Senior Notes [Member]          
Debt Instrument [Line Items]          
Maximum Leverage Ratio     60.00%    
Maximum Secured Debt Leverage Ratio     50.00%    
Minimum Interest Coverage Ratio     1.50    
Minimum Unencumbered Asset Value Percentage Of Unsecured Debt     150.00%    
Boston Properties Limited Partnership          
Debt Instrument [Line Items]          
Loss on Extinguishment of Debt     $ (496) 371 22,040
Repayments of Unsecured Debt     848,020 0 0
Proceeds from unsecured senior notes     847,935 $ 1,989,790 $ 0
Boston Properties Limited Partnership | Senior Notes [Member]          
Debt Instrument [Line Items]          
Long-term Debt, Gross     $ 7,300,000    
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.35% [Member]          
Debt Instrument [Line Items]          
Coupon/Stated Rate   3.20% 3.20%    
Senior Notes Pricing   99.757%      
Effective Rate   3.35% 3.35% [1]    
Proceeds from unsecured senior notes   $ 841,100      
Debt Instrument, Face Amount   $ 850,000      
Long-term Debt, Gross     $ 850,000    
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.853%          
Debt Instrument [Line Items]          
Debt Instrument, Increase, Accrued Interest $ 2,800        
Debt Instrument, Redemption Price, Percentage 101.49%        
Loss on Extinguishment of Debt $ 13,900        
Redemption Premium $ 12,700        
Coupon/Stated Rate 3.70%        
Repayments of Unsecured Debt $ 865,500        
Debt Instrument, Face Amount $ 850,000        
[1] Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.