Summary Of Significant Accounting Policies (Narrative) (Details) $ in Thousands		6 Months Ended
	Jan. 01, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of VIEs		6
Number of VIEs - Total		7
Cumulative effect of a change in accounting principle		$ (1,679)	$ (4,379)
Dividends In Excess Of Earnings [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of a change in accounting principle	$ 1,500	(1,505)	(3,864)
Dividends In Excess Of Earnings [Member] | Boston Properties Limited Partnership
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of a change in accounting principle	1,500
Noncontrolling Interests [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of a change in accounting principle	200	(174)	(445)
Noncontrolling Interests [Member] | Boston Properties Limited Partnership
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of a change in accounting principle	$ 200
Noncontrolling interest - property partnerships [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of a change in accounting principle		$ 0	$ (70)