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Unsecured Senior Notes Unsecured Senior Notes (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 13, 2018
Nov. 28, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]          
Loss on Extinguishment of Debt     $ 16,490 $ (496) $ 371
Repayments of Unsecured Debt     699,517 848,020 0
Proceeds from unsecured senior notes     $ 996,410 847,935 1,989,790
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     $ 16,490 (496) 371
Repayments of Unsecured Debt     699,517 848,020 0
Proceeds from unsecured senior notes     $ 996,410 $ 847,935 $ 1,989,790
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 4.628%          
Debt Instrument [Line Items]          
Coupon/Stated Rate   4.50% 4.50%    
Senior Notes Pricing   99.641%      
Effective Rate   4.628% 4.628% [1]    
Proceeds from unsecured senior notes   $ 988,100      
Debt Instrument, Face Amount   $ 1,000,000      
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 5.967%          
Debt Instrument [Line Items]          
Debt Instrument, Increase, Accrued Interest $ 6,600        
Debt Instrument, Redemption Price, Percentage 102.28%        
Loss on Extinguishment of Debt $ 16,500        
Redemption Premium $ 16,000        
Coupon/Stated Rate 5.875%        
Repayments of Unsecured Debt $ 722,600        
Debt Instrument, Face Amount $ 700,000        
[1] Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.