Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2023		Sep. 30, 2022		Sep. 30, 2023		Sep. 30, 2022
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 785,820	[1]	$ 753,069	[1]	$ 2,331,442	[2]	$ 2,215,290	[2]
Rental Revenue: Residential	11,789	[1]	14,340	[1]	35,768	[2]	44,218	[2]
Rental Revenue Total	$ 811,093	[1]	$ 779,158	[1]	$ 2,402,764	[2]	$ 2,287,903	[2]
Rental Revenue: % of Grand Totals	100.00%		100.00%		100.00%		100.00%
Rental Expenses: Class A Office	$ 294,454		$ 274,678		$ 865,552		$ 802,531
Rental Expenses: Residential	5,738		7,024		16,984		23,274
Rental Expenses: Total	$ 309,212		$ 290,250		$ 906,388		$ 845,637
Rental Expenses: % Of Grand Totals	100.00%		100.00%		100.00%		100.00%
Net Operating Income	$ 501,881		$ 488,908		$ 1,496,376		$ 1,442,266
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	$ 276,153	[1]	$ 255,958	[1]	$ 815,568	[2]	$ 742,972	[2]
Rental Revenue: Residential	4,198	[1]	3,837	[1]	12,371	[2]	11,181	[2]
Rental Revenue Total	$ 293,835	[1]	$ 271,544	[1]	$ 863,493	[2]	$ 782,548	[2]
Rental Revenue: % of Grand Totals	36.23%		34.85%		35.95%		34.20%
Rental Expenses: Class A Office	$ 97,358		$ 91,226		$ 293,004		$ 268,781
Rental Expenses: Residential	1,629		1,552		4,782		4,481
Rental Expenses: Total	$ 108,007		$ 101,326		$ 321,638		$ 293,094
Rental Expenses: % Of Grand Totals	34.94%		34.91%		35.49%		34.66%
Net Operating Income	$ 185,828		$ 170,218		$ 541,855		$ 489,454
Net Operating Income: % of Grand Totals	37.03%		34.81%		36.22%		33.94%
Company's Share of Net Operating Income: % of Grand Totals	37.07%		35.12%		36.19%		34.18%
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	2.55%		2.76%		2.61%		2.85%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 268,680	[1]	$ 260,926	[1]	$ 789,851	[2]	$ 772,060	[2]
Rental Revenue: Residential	0	[1]	0	[1]	0	[2]	0	[2]
Rental Revenue Total	$ 268,680	[1]	$ 260,926	[1]	$ 789,851	[2]	$ 772,060	[2]
Rental Revenue: % of Grand Totals	33.13%		33.49%		32.87%		33.75%
Rental Expenses: Class A Office	$ 107,462		$ 99,942		$ 312,895		$ 291,645
Rental Expenses: Residential	0		0		0		0
Rental Expenses: Total	$ 107,462		$ 99,942		$ 312,895		$ 291,645
Rental Expenses: % Of Grand Totals	34.75%		34.43%		34.52%		34.49%
Net Operating Income	$ 161,218		$ 160,984		$ 476,956		$ 480,415
Net Operating Income: % of Grand Totals	32.12%		32.93%		31.87%		33.31%
Company's Share of Net Operating Income: % of Grand Totals	25.84%		25.99%		25.57%		26.38%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 135,839	[1]	$ 134,938	[1]	$ 408,173	[2]	$ 401,020	[2]
Rental Revenue: Residential	3,214	[1]	3,133	[1]	10,720	[2]	11,374	[2]
Rental Revenue Total	$ 139,053	[1]	$ 138,071	[1]	$ 418,893	[2]	$ 412,394	[2]
Rental Revenue: % of Grand Totals	17.14%		17.72%		17.43%		18.02%
Rental Expenses: Class A Office	$ 50,450		$ 47,068		$ 144,732		$ 135,677
Rental Expenses: Residential	2,221		2,125		6,609		9,138
Rental Expenses: Total	$ 52,671		$ 49,193		$ 151,341		$ 144,815
Rental Expenses: % Of Grand Totals	17.03%		16.95%		16.70%		17.12%
Net Operating Income	$ 86,382		$ 88,878		$ 267,552		$ 267,579
Net Operating Income: % of Grand Totals	17.21%		18.18%		17.88%		18.55%
Company's Share of Net Operating Income: % of Grand Totals	18.41%		19.35%		18.89%		19.69%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 13,660	[1]	$ 12,293		$ 44,978	[2]	$ 18,765	[2]
Rental Revenue: Residential	0	[1]	0		0	[2]	0	[2]
Rental Revenue Total	$ 13,660	[1]	$ 12,293		$ 44,978	[2]	$ 18,765	[2]
Rental Revenue: % of Grand Totals	1.68%		1.58%		1.87%		0.82%
Rental Expenses: Class A Office	$ 2,971		$ 3,125		$ 9,013		$ 4,805
Rental Expenses: Residential	0		0		0		0
Rental Expenses: Total	$ 2,971		$ 3,125		$ 9,013		$ 4,805
Rental Expenses: % Of Grand Totals	0.96%		1.08%		0.99%		0.57%
Net Operating Income	$ 10,689		$ 9,168		$ 35,965		$ 13,960
Net Operating Income: % of Grand Totals	2.13%		1.88%		2.40%		0.97%
Company's Share of Net Operating Income: % of Grand Totals	2.56%		2.34%		2.82%		1.41%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 91,488	[1]	$ 88,954	[1]	$ 272,872	[2]	$ 280,473	[2]
Rental Revenue: Residential	4,377	[1]	7,370	[1]	12,677	[2]	21,663	[2]
Rental Revenue Total	$ 95,865	[1]	$ 96,324	[1]	$ 285,549	[2]	$ 302,136	[2]
Rental Revenue: % of Grand Totals	11.82%		12.36%		11.88%		13.21%
Rental Expenses: Class A Office	$ 36,213		$ 33,317		$ 105,908		$ 101,623
Rental Expenses: Residential	1,888		3,347		5,593		9,655
Rental Expenses: Total	$ 38,101		$ 36,664		$ 111,501		$ 111,278
Rental Expenses: % Of Grand Totals	12.32%		12.63%		12.30%		13.16%
Net Operating Income	$ 57,764		$ 59,660		$ 174,048		$ 190,858
Net Operating Income: % of Grand Totals	11.51%		12.20%		11.63%		13.23%
Company's Share of Net Operating Income: % of Grand Totals	13.57%		14.44%		13.92%		15.49%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	$ 13,484	[1]	$ 11,749	[1]	$ 35,554	[2]	$ 28,395	[2]
Operating expense	9,020		8,548		23,852		19,832
Hotel [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	13,484	[1]	11,749	[1]	35,554	[2]	28,395	[2]
Operating expense	9,020		8,548		23,852		19,832
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	(50,047)		(48,306)		(145,102)		(143,223)
Noncontrolling interest - property partnerships [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(11,786)		(11,293)		(33,946)		(34,405)
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	(38,261)		(37,013)		(111,156)		(108,818)
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	7,946		8,169		25,294		25,996
Unconsolidated Joint Ventures [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	12,508		13,143		38,501		40,147
Unconsolidated Joint Ventures [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	3,938		(259)		10,951		(397)
Unconsolidated Joint Ventures [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	4,023		3,233		10,819		9,597
Unconsolidated Joint Ventures [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income	1,874		1,978		5,598		5,877
Unconsolidated Joint Ventures [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	8,876		9,052		31,012		27,127
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income	490,999		475,918		1,473,449		1,407,390
Company's Share [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	181,988		167,094		533,203		481,045
Company's Share [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	12,508		13,143		38,501		40,147
Company's Share [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	126,895		123,712		376,751		371,200
Company's Share [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	90,405		92,111		278,371		277,176
Company's Share [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income	12,563		11,146		41,563		19,837
Company's Share [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	$ 66,640		$ 68,712		$ 205,060		$ 217,985

[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.