Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Interest capitalized	$ 53,097,000	$ 53,881,000	$ 54,911,000
Salaries And Related Costs Capitalized	13,700,000	12,900,000	10,400,000
Cash FDIC Insured Limit	250,000
Separate Unrestricted Cash For Deferred Compensation Plan.	43,600,000	39,500,000
Gains from investments in securities	5,626,000	5,261,000	6,417,000
Straight Line Rent Adjustments	104,300,000	104,900,000	58,400,000
Above and below market rent adjustments, net	4,200,000	6,500,000	20,900,000
Impairment loss	0	0	24,038,000
Boston Properties Limited Partnership
Summary Of Significant Accounting Policies [Line Items]
Interest capitalized	53,097,000	53,881,000	54,911,000
Gains from investments in securities	5,626,000	5,261,000	6,417,000
Impairment loss	$ 0	$ 0	22,272,000
one tower center
Summary Of Significant Accounting Policies [Line Items]
Impairment loss			24,000,000
one tower center | Boston Properties Limited Partnership
Summary Of Significant Accounting Policies [Line Items]
Impairment loss			$ 22,300,000