Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 808,122	$ 769,158
Rental Revenue: Residential	[1]	12,684	11,726
Rental Revenue Total	[1]	$ 828,992	$ 788,985
Rental Revenue: % of Grand Totals		100.00%	100.00%
Rental Expenses: Class A Office		$ 308,471	$ 285,845
Rental Expenses: Residential		5,686	5,463
Rental Expenses: Total		$ 320,172	$ 297,979
Rental Expenses: % Of Grand Totals		100.00%	100.00%
Net Operating Income		$ 508,820	$ 491,006
Net Operating Income: % of Grand Totals		100.00%	100.00%
Company's Share of Net Operating Income: % of Grand Totals		100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 280,466	$ 269,951
Rental Revenue: Residential	[1]	4,196	4,049
Rental Revenue Total	[1]	$ 292,848	$ 282,101
Rental Revenue: % of Grand Totals		35.33%	35.76%
Rental Expenses: Class A Office		$ 105,171	$ 100,049
Rental Expenses: Residential		1,593	1,552
Rental Expenses: Total		$ 112,779	$ 108,272
Rental Expenses: % Of Grand Totals		35.23%	36.34%
Net Operating Income		$ 180,069	$ 173,829
Net Operating Income: % of Grand Totals		35.39%	35.41%
Company's Share of Net Operating Income: % of Grand Totals		35.71%	35.41%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 20,401	$ 0
Rental Revenue: Residential	[1]	0	0
Rental Revenue Total	[1]	$ 20,401	$ 0
Rental Revenue: % of Grand Totals		2.46%	0.00%
Rental Expenses: Class A Office		$ 6,567	$ 0
Rental Expenses: Residential		0	0
Rental Expenses: Total		$ 6,567	$ 0
Rental Expenses: % Of Grand Totals		2.05%	0.00%
Net Operating Income		$ 13,834	$ 0
Net Operating Income: % of Grand Totals		2.72%	0.00%
Company's Share of Net Operating Income: % of Grand Totals		4.24%	2.73%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 260,809	$ 258,192
Rental Revenue: Residential	[1]	0	0
Rental Revenue Total	[1]	$ 260,809	$ 258,192
Rental Revenue: % of Grand Totals		31.46%	32.72%
Rental Expenses: Class A Office		$ 107,481	$ 102,485
Rental Expenses: Residential		0	0
Rental Expenses: Total		$ 107,481	$ 102,485
Rental Expenses: % Of Grand Totals		33.57%	34.39%
Net Operating Income		$ 153,328	$ 155,707
Net Operating Income: % of Grand Totals		30.13%	31.71%
Company's Share of Net Operating Income: % of Grand Totals		24.88%	25.39%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 132,614	$ 136,093
Rental Revenue: Residential	[1]	3,958	3,642
Rental Revenue Total	[1]	$ 136,572	$ 139,735
Rental Revenue: % of Grand Totals		16.47%	17.71%
Rental Expenses: Class A Office		$ 46,942	$ 46,085
Rental Expenses: Residential		2,218	2,173
Rental Expenses: Total		$ 49,160	$ 48,258
Rental Expenses: % Of Grand Totals		15.35%	16.20%
Net Operating Income		$ 87,412	$ 91,477
Net Operating Income: % of Grand Totals		17.18%	18.63%
Company's Share of Net Operating Income: % of Grand Totals		18.60%	19.59%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 10,910	$ 14,258
Rental Revenue: Residential	[1]	0	0
Rental Revenue Total	[1]	$ 10,910	$ 14,258
Rental Revenue: % of Grand Totals		1.32%	1.81%
Rental Expenses: Class A Office		$ 3,081	$ 2,960
Rental Expenses: Residential		0	0
Rental Expenses: Total		$ 3,081	$ 2,960
Rental Expenses: % Of Grand Totals		0.96%	0.99%
Net Operating Income		$ 7,829	$ 11,298
Net Operating Income: % of Grand Totals		1.54%	2.30%
Company's Share of Net Operating Income: % of Grand Totals		1.95%	2.71%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 102,922	$ 90,664
Rental Revenue: Residential	[1]	4,530	4,035
Rental Revenue Total	[1]	$ 107,452	$ 94,699
Rental Revenue: % of Grand Totals		12.96%	12.00%
Rental Expenses: Class A Office		$ 39,229	$ 34,266
Rental Expenses: Residential		1,875	1,738
Rental Expenses: Total		$ 41,104	$ 36,004
Rental Expenses: % Of Grand Totals		12.84%	12.08%
Net Operating Income		$ 66,348	$ 58,695
Net Operating Income: % of Grand Totals		13.04%	11.95%
Company's Share of Net Operating Income: % of Grand Totals		14.62%	14.17%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	$ 8,186	$ 8,101
Operating expense		6,015	6,671
Hotel [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	8,186	8,101
Operating expense		6,015	6,671
Hotel [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0
Operating expense		0	0
Hotel [Member] | New York [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0
Operating expense		0	0
Hotel [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0
Operating expense		0	0
Hotel [Member] | Seattle
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0
Operating expense		0	0
Hotel [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0	0
Operating expense		0	0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(46,570)	(47,097)
Noncontrolling interest - property partnerships [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(11,056)	(10,817)
Noncontrolling interest - property partnerships [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	0
Noncontrolling interest - property partnerships [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(35,514)	(36,280)
Noncontrolling interest - property partnerships [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	0
Noncontrolling interest - property partnerships [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		0	0
Noncontrolling interest - property partnerships [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		0	0
Unconsolidated Joint Ventures [Member]
Segment Reporting Information [Line Items]
Net Operating Income		35,430	40,756
Unconsolidated Joint Ventures [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		8,757	8,577
Unconsolidated Joint Ventures [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		7,248	13,225
Unconsolidated Joint Ventures [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		5,984	3,650
Unconsolidated Joint Ventures [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		5,154	3,464
Unconsolidated Joint Ventures [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		1,876	1,846
Unconsolidated Joint Ventures [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		6,411	9,994
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income		497,680	484,665
Company's Share [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		177,770	171,589
Company's Share [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		21,082	13,225
Company's Share [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		123,798	123,077
Company's Share [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		92,566	94,941
Company's Share [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		9,705	13,144
Company's Share [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		$ 72,759	$ 68,689

[1] Rental Revenue is equal to Total Revenue per the Company’s Consolidated Statements of Operations, less Development and Management Services Revenue and Direct Reimbursements of Payroll and Related Costs from Management Services Contracts Revenue per the Consolidated Statements of Operations.