Summary Of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) yr	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Entity Information [Line Items]
Probable Sale Term of Property After Classified As Held For Sale (Years) | yr	1
Maximum Period After Construction The Company Considers A Construction Project As Substantially Completed (In Years) | yr	1
Interest costs capitalized	$ 61,070,000	$ 39,237,000	$ 34,213,000
Salaries And Related Costs Capitalized	13,200,000	11,100,000	10,400,000
Cash FDIC Insured Limit	250,000
Separate Unrestricted Cash For Deferred Compensation Plan.	29,200,000	23,800,000
Gains (losses) from investments in securities	3,678,000	2,273,000	(653,000)
Internal Leasing Salaries And Related Costs Capitalized	5,000,000	7,200,000	5,500,000
Straight-line rent adjustments	(54,800,000)	(31,700,000)	(80,000,000)
Above and below market rent adjustments, net	$ 23,500,000	30,200,000	35,900,000
Ground Lease Expiration Date, Maximum	2114
REIT Annual Taxable Income Distribution Requirement Percentage, Minimum	90.00%
Company Annual Taxable Income Distribution Percentage	100.00%
Net Difference Between Tax Basis And Company's Assets And Liabilities.	$ 1,800,000,000	1,700,000,000
Debt Issuance Costs, Net	34,680,000
Cumulative effect of a change in accounting principle	2,035,000
Boston Properties Limited Partnership
Entity Information [Line Items]
Interest costs capitalized	61,070,000	39,237,000	34,213,000
Gains (losses) from investments in securities	3,678,000	2,273,000	$ (653,000)
Net Difference Between Tax Basis And Company's Assets And Liabilities.	2,900,000,000	$ 2,700,000,000
Debt Issuance Costs, Net	34,700,000
Cumulative effect of a change in accounting principle	272,000
Dividends In Excess Of Earnings [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle	272,000
Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle	1,763,000
Noncontrolling Interests [Member] | Boston Properties Limited Partnership
Entity Information [Line Items]
Cumulative effect of a change in accounting principle	$ 1,763,000