Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023		Jun. 30, 2022		Jun. 30, 2023		Jun. 30, 2022
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 776,464	[1]	$ 735,333	[1]	$ 1,545,622	[2]	$ 1,462,221	[2]
Rental Revenue: Residential	12,253	[1]	16,912	[1]	23,979	[2]	29,878	[2]
Rental Revenue Total	$ 802,686	[1]	$ 764,334	[1]	$ 1,591,671	[2]	$ 1,508,745	[2]
Rental Revenue: % of Grand Totals	100.00%		100.00%		100.00%		100.00%
Rental Expenses: Class A Office	$ 285,253		$ 264,030		$ 571,098		$ 527,853
Rental Expenses: Residential	5,783		9,818		11,246		16,250
Rental Expenses: Total	$ 299,197		$ 280,292		$ 597,176		$ 555,387
Rental Expenses: % Of Grand Totals	100.00%		100.00%		100.00%		100.00%
Net Operating Income	$ 503,489		$ 484,042		$ 994,495		$ 953,358
Net Operating Income: % of Grand Totals	100.00%		100.00%		100.00%		100.00%
Company's Share of Net Operating Income: % of Grand Totals	100.00%		100.00%		100.00%		100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 269,464	[1]	$ 244,936	[1]	$ 539,415	[2]	$ 487,014	[2]
Rental Revenue: Residential	4,124	[1]	3,748	[1]	8,173	[2]	7,344	[2]
Rental Revenue Total	$ 287,557	[1]	$ 260,773	[1]	$ 569,658	[2]	$ 511,004	[2]
Rental Revenue: % of Grand Totals	35.83%		34.11%		35.79%		33.87%
Rental Expenses: Class A Office	$ 95,597		$ 87,027		$ 195,646		$ 177,555
Rental Expenses: Residential	1,601		1,492		3,153		2,929
Rental Expenses: Total	$ 105,359		$ 94,963		$ 213,631		$ 191,768
Rental Expenses: % Of Grand Totals	35.21%		33.88%		35.78%		34.53%
Net Operating Income	$ 182,198		$ 165,810		$ 356,027		$ 319,236
Net Operating Income: % of Grand Totals	36.19%		34.25%		35.80%		33.49%
Company's Share of Net Operating Income: % of Grand Totals	36.08%		34.44%		35.75%		33.70%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 0	[1]	$ 0	[1]	$ 0	[2]	$ 0	[2]
Rental Revenue: Residential	0	[1]	0	[1]	0	[2]	0	[2]
Rental Revenue Total	$ 0	[1]	$ 0	[1]	$ 0	[2]	$ 0	[2]
Rental Revenue: % of Grand Totals	0.00%		0.00%		0.00%		0.00%
Rental Expenses: Class A Office	$ 0		$ 0		$ 0		$ 0
Rental Expenses: Residential	0		0		0		0
Rental Expenses: Total	$ 0		$ 0		$ 0		$ 0
Rental Expenses: % Of Grand Totals	0.00%		0.00%		0.00%		0.00%
Net Operating Income	$ 0		$ 0		$ 0		$ 0
Net Operating Income: % of Grand Totals	0.00%		0.00%		0.00%		0.00%
Company's Share of Net Operating Income: % of Grand Totals	2.56%		2.81%		2.65%		2.90%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 262,979	[1]	$ 254,264	[1]	$ 521,171	[2]	$ 511,134	[2]
Rental Revenue: Residential	0	[1]	0	[1]	0	[2]	0	[2]
Rental Revenue Total	$ 262,979	[1]	$ 254,264	[1]	$ 521,171	[2]	$ 511,134	[2]
Rental Revenue: % of Grand Totals	32.76%		33.27%		32.74%		33.88%
Rental Expenses: Class A Office	$ 102,948		$ 95,363		$ 205,433		$ 191,703
Rental Expenses: Residential	0		0		0		0
Rental Expenses: Total	$ 102,948		$ 95,363		$ 205,433		$ 191,703
Rental Expenses: % Of Grand Totals	34.41%		34.02%		34.40%		34.52%
Net Operating Income	$ 160,031		$ 158,901		$ 315,738		$ 319,431
Net Operating Income: % of Grand Totals	31.78%		32.83%		31.75%		33.51%
Company's Share of Net Operating Income: % of Grand Totals	25.47%		25.95%		25.43%		26.57%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 136,241	[1]	$ 133,707	[1]	$ 272,334	[2]	$ 266,082	[2]
Rental Revenue: Residential	3,864	[1]	5,850	[1]	7,506	[2]	8,241	[2]
Rental Revenue Total	$ 140,105	[1]	$ 139,557	[1]	$ 279,840	[2]	$ 274,323	[2]
Rental Revenue: % of Grand Totals	17.45%		18.26%		17.58%		18.18%
Rental Expenses: Class A Office	$ 48,197		$ 45,201		$ 94,282		$ 88,609
Rental Expenses: Residential	2,215		5,145		4,388		7,013
Rental Expenses: Total	$ 50,412		$ 50,346		$ 98,670		$ 95,622
Rental Expenses: % Of Grand Totals	16.85%		17.96%		16.52%		17.22%
Net Operating Income	$ 89,693		$ 89,211		$ 181,170		$ 178,701
Net Operating Income: % of Grand Totals	17.81%		18.43%		18.22%		18.74%
Company's Share of Net Operating Income: % of Grand Totals	18.69%		19.58%		19.13%		19.87%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 17,060	[1]	$ 6,472		$ 31,318	[2]	$ 6,472	[2]
Rental Revenue: Residential	0	[1]	0		0	[2]	0	[2]
Rental Revenue Total	$ 17,060	[1]	$ 6,472		$ 31,318	[2]	$ 6,472	[2]
Rental Revenue: % of Grand Totals	2.13%		0.85%		1.97%		0.43%
Rental Expenses: Class A Office	$ 3,082		$ 1,680		$ 6,042		$ 1,680
Rental Expenses: Residential	0		0		0		0
Rental Expenses: Total	$ 3,082		$ 1,680		$ 6,042		$ 1,680
Rental Expenses: % Of Grand Totals	1.03%		0.60%		1.01%		0.30%
Net Operating Income	$ 13,978		$ 4,792		$ 25,276		$ 4,792
Net Operating Income: % of Grand Totals	2.78%		0.99%		2.54%		0.50%
Company's Share of Net Operating Income: % of Grand Totals	3.19%		1.43%		2.95%		0.93%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 90,720	[1]	$ 95,954	[1]	$ 181,384	[2]	$ 191,519	[2]
Rental Revenue: Residential	4,265	[1]	7,314	[1]	8,300	[2]	14,293	[2]
Rental Revenue Total	$ 94,985	[1]	$ 103,268	[1]	$ 189,684	[2]	$ 205,812	[2]
Rental Revenue: % of Grand Totals	11.83%		13.51%		11.92%		13.64%
Rental Expenses: Class A Office	$ 35,429		$ 34,759		$ 69,695		$ 68,306
Rental Expenses: Residential	1,967		3,181		3,705		6,308
Rental Expenses: Total	$ 37,396		$ 37,940		$ 73,400		$ 74,614
Rental Expenses: % Of Grand Totals	12.50%		13.54%		12.29%		13.43%
Net Operating Income	$ 57,589		$ 65,328		$ 116,284		$ 131,198
Net Operating Income: % of Grand Totals	11.44%		13.50%		11.69%		13.76%
Company's Share of Net Operating Income: % of Grand Totals	14.01%		15.79%		14.09%		16.03%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	$ 13,969	[1]	$ 12,089	[1]	$ 22,070	[2]	$ 16,646	[2]
Operating expense	8,161		6,444		14,832		11,284
Hotel [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	13,969	[1]	12,089	[1]	22,070	[2]	16,646	[2]
Operating expense	8,161		6,444		14,832		11,284
Hotel [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	0	[1]	0	[1]	0	[2]	0	[2]
Operating expense	0		0		0		0
Hotel [Member] | New York [Member]
Segment Reporting Information [Line Items]
Other revenue	0	[1]	0	[1]	0	[2]	0	[2]
Operating expense	0		0		0		0
Hotel [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	0	[1]	0	[1]	0	[2]	0	[2]
Operating expense	0		0		0		0
Hotel [Member] | Seattle
Segment Reporting Information [Line Items]
Other revenue	0	[1]	0		0	[2]	0	[2]
Operating expense	0		0		0		0
Hotel [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	0	[1]	0	[1]	0	[2]	0	[2]
Operating expense	0		0		0		0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(47,958)		(47,862)		(95,055)		(94,917)
Noncontrolling interest - property partnerships [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(11,343)		(11,377)		(22,160)		(23,112)
Noncontrolling interest - property partnerships [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	0		0		0		0
Noncontrolling interest - property partnerships [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(36,615)		(36,485)		(72,895)		(71,805)
Noncontrolling interest - property partnerships [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	0		0		0		0
Noncontrolling interest - property partnerships [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income	0		0		0		0
Noncontrolling interest - property partnerships [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	0		0		0		0
Unconsolidated Joint Ventures [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	8,771		8,134		17,348		17,827
Unconsolidated Joint Ventures [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	12,768		13,247		25,993		27,004
Unconsolidated Joint Ventures [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	3,363		18		7,013		(138)
Unconsolidated Joint Ventures [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	3,332		3,183		6,796		6,364
Unconsolidated Joint Ventures [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income	1,878		1,944		3,724		3,899
Unconsolidated Joint Ventures [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	12,142		9,184		22,136		18,075
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income	497,785		471,890		982,450		931,472
Company's Share [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	179,626		162,567		351,215		313,951
Company's Share [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	12,768		13,247		25,993		27,004
Company's Share [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	126,779		122,434		249,856		247,488
Company's Share [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	93,025		92,394		187,966		185,065
Company's Share [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income	15,856		6,736		29,000		8,691
Company's Share [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	$ 69,731		$ 74,512		$ 138,420		$ 149,273

[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.

[2] 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.