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Summary Of Significant Accounting Policies (Narrative) (Details)
 3 Months Ended 12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2019
USD ($)
yr
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Jan. 01, 2019
USD ($)
Entity Information [Line Items]          
Probable Sale Term of Property After Classified As Held For Sale (Years) | yr   1      
Interest costs capitalized   $ 54,911,000 $ 65,766,000 $ 61,070,000  
Salaries And Related Costs Capitalized   10,400,000 12,500,000 13,200,000  
Cash FDIC Insured Limit $ 250,000 250,000      
Separate Unrestricted Cash For Deferred Compensation Plans 36,700,000 36,700,000 28,200,000    
Gains (losses) from investments in securities   6,417,000 (1,865,000) 3,678,000  
Internal Leasing Salaries And Related Costs Capitalized     5,400,000 5,000,000.0  
Straight-line rent adjustments   58,400,000 51,900,000 54,800,000  
Above and below market rent adjustments, net   $ 20,900,000 23,800,000 23,500,000  
REIT Annual Taxable Income Distribution Requirement Percentage, Minimum   90.00%      
Company Annual Taxable Income Distribution Percentage   100.00%      
Cumulative effect of a change in accounting principle   $ 4,379,000 (5,496,000) 2,035,000  
Right of use assets - operating leases 148,640,000 148,640,000     $ 151,800,000
Operating Lease, Liability 200,180,000 200,180,000     $ 199,300,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount 8,365,000 8,365,000      
Accounts Payable and Accrued Liabilities $ 377,553,000 377,553,000 276,645,000    
Lessee, Finance Lease, Description four        
Boston Properties Limited Partnership          
Entity Information [Line Items]          
Interest costs capitalized   54,911,000 65,766,000 61,070,000  
Gains (losses) from investments in securities   6,417,000 (1,865,000) 3,678,000  
Right of use assets - operating leases $ 148,640,000 148,640,000      
Operating Lease, Liability 200,180,000 200,180,000      
Redeemable Noncontrolling Interest, Equity, Carrying Amount 8,365,000 8,365,000      
Accounts Payable and Accrued Liabilities 377,553,000 377,553,000 276,645,000    
deferred compenstation for directors [Member]          
Entity Information [Line Items]          
Change in classification of director deferred compensation plan   8,400,000      
Redeemable Noncontrolling Interest, Equity, Carrying Amount 8,100,000 8,100,000      
Accounts Payable and Accrued Liabilities $ 300,000 300,000      
Dividends In Excess Of Earnings [Member]          
Entity Information [Line Items]          
Cumulative effect of a change in accounting principle   3,864,000 (4,933,000) 272,000  
Noncontrolling Interests [Member]          
Entity Information [Line Items]          
Cumulative effect of a change in accounting principle   445,000 $ (563,000) $ 1,763,000  
Noncontrolling interest - property partnerships [Member]          
Entity Information [Line Items]          
Cumulative effect of a change in accounting principle   $ 70,000