Summary Of Significant Accounting Policies (Narrative) (Details)		3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) yr	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Entity Information [Line Items]
Maximum Period After Construction The Company Considers A Construction Project As Substantially Completed (In Years) | yr				1
Interest costs capitalized				$ 65,766,000	$ 61,070,000	$ 39,200,000
Salaries And Related Costs Capitalized				12,500,000	13,200,000	11,100,000
Cash FDIC Insured Limit		$ 250,000		250,000
Separate Unrestricted Cash For Deferred Compensation Plan.		28,200,000		28,200,000	29,200,000
Gains (losses) from investments in securities				(1,865,000)	3,678,000	2,273,000
Internal Leasing Salaries And Related Costs Capitalized				5,400,000	5,000,000	7,200,000
Straight-line rent adjustments				(51,900,000)	(54,800,000)	(31,700,000)
Above and below market rent adjustments, net				$ 23,800,000	23,500,000	30,200,000
Ground Lease Expiration Date, Maximum				2114
REIT Annual Taxable Income Distribution Requirement Percentage, Minimum				90.00%
Company Annual Taxable Income Distribution Percentage				100.00%
Debt Issuance Costs, Net		30,756,000		$ 30,756,000
Cumulative effect of a change in accounting principle				(5,496,000)	2,035,000
Payroll and related costs from management services contracts				9,590,000	0	0
Direct reimbursements of payroll and related costs from management services contracts				9,590,000	0	0
Net Cash Provided by (Used in) Operating Activities				1,150,245,000	911,979,000	1,034,548,000
Net Cash Provided by (Used in) Investing Activities				1,098,876,000	882,044,000	1,337,347,000
Net Cash Provided by (Used in) Financing Activities				82,453,000	55,346,000	(74,621,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		639,191,000		639,191,000	505,369,000	420,088,000	$ 797,508,000
Interest Expense				378,168,000	374,481,000	412,849,000
Boston Properties Limited Partnership
Entity Information [Line Items]
Interest costs capitalized				65,766,000	61,070,000	39,237,000
Gains (losses) from investments in securities				(1,865,000)	3,678,000	2,273,000
Debt Issuance Costs, Net		30,800,000		30,800,000
Cumulative effect of a change in accounting principle				(4,933,000)	272,000
Payroll and related costs from management services contracts				9,590,000	0	0
Direct reimbursements of payroll and related costs from management services contracts				9,590,000	0	0
Net Cash Provided by (Used in) Operating Activities				1,150,245,000	911,979,000	1,034,548,000
Net Cash Provided by (Used in) Investing Activities				1,098,876,000	882,044,000	1,337,347,000
Net Cash Provided by (Used in) Financing Activities				82,453,000	55,346,000	(74,621,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		639,191,000		639,191,000	505,369,000	420,088,000	$ 797,508,000
Interest Expense				378,168,000	374,481,000	412,849,000
Dividends In Excess Of Earnings [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle				(4,933,000)	272,000
Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle				(563,000)	1,763,000
Noncontrolling Interests [Member] | Boston Properties Limited Partnership
Entity Information [Line Items]
Cumulative effect of a change in accounting principle				(563,000)	1,763,000
Accounting Standards Update 2014-09 [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			$ (4,900,000)
Accounting Standards Update 2014-09 [Member] | Noncontrolling Interests [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle			$ (600,000)
Accounting Standards Update 2016-15 [Member]
Entity Information [Line Items]
Non Cash Portion Of Loss From Early Extinguishment Of Debt				$ 16,000,000	12,800,000
Accounting Standards Update 2016-18 [Member]
Entity Information [Line Items]
Net Cash Provided by (Used in) Operating Activities					4,500,000	(2,300,000)
Net Cash Provided by (Used in) Investing Activities					(15,800,000)	8,300,000
Net Cash Provided by (Used in) Financing Activities					(12,900,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents					$ 7,400,000	$ 10,600,000
Accounting Standards Update 2017-12 [Member]
Entity Information [Line Items]
Interest Expense		$ 1,700,000
Subsequent Event [Member] | Accounting Standards Update 2016-02 [Member]
Entity Information [Line Items]
Cumulative effect of a change in accounting principle	$ (4,000,000)
Operating Lease, Right-of-Use Asset	148,800,000
Operating Lease, Liability	$ 199,700,000