Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2022		Sep. 30, 2021	Sep. 30, 2022		Sep. 30, 2021
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 753,069		$ 704,873	$ 2,215,290		$ 2,090,997
Rental Revenue: Residential	[1]	14,340		10,894	44,218		29,832
Rental Revenue Total	[1]	$ 779,158		$ 720,956	$ 2,287,903		$ 2,128,211
Rental Revenue: % of Grand Totals		100.00%		100.00%	100.00%		100.00%
Rental Expenses: Class A Office		$ 274,678		$ 252,236	$ 802,531		$ 746,273
Rental Expenses: Residential		7,024		6,045	23,274		18,100
Rental Expenses: Total		$ 290,250		$ 262,227	$ 845,637		$ 772,366
Rental Expenses: % Of Grand Totals		100.00%		100.00%	100.00%		100.00%
Net Operating Income		$ 488,908		$ 458,729	$ 1,442,266		$ 1,355,845
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	[1]	$ 255,958		$ 236,080	$ 742,972		$ 696,054
Rental Revenue: Residential	[1]	3,837		3,418	11,181		9,594
Rental Revenue Total	[1]	$ 271,544		$ 244,687	$ 782,548		$ 713,030
Rental Revenue: % of Grand Totals		34.85%		33.93%	34.20%		33.50%
Rental Expenses: Class A Office		$ 91,226		$ 82,697	$ 268,781		$ 240,743
Rental Expenses: Residential		1,552		1,396	4,481		4,286
Rental Expenses: Total		$ 101,326		$ 88,039	$ 293,094		$ 253,022
Rental Expenses: % Of Grand Totals		34.91%		33.57%	34.66%		32.76%
Net Operating Income		$ 170,218		$ 156,648	$ 489,454		$ 460,008
Net Operating Income: % of Grand Totals		34.81%		34.15%	33.94%		33.93%
Company's Share of Net Operating Income: % of Grand Totals		35.12%		34.30%	34.18%		33.88%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 0		$ 0	$ 0		$ 0
Rental Revenue: Residential	[1]	0		0	0		0
Rental Revenue Total	[1]	$ 0		$ 0	$ 0		$ 0
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		2.76%		2.78%	2.85%		2.98%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 260,926		$ 257,656	$ 772,060		$ 760,002
Rental Revenue: Residential	[1]	0		0	0		0
Rental Revenue Total	[1]	$ 260,926		$ 257,656	$ 772,060		$ 760,002
Rental Revenue: % of Grand Totals		33.49%		35.74%	33.75%		35.71%
Rental Expenses: Class A Office		$ 99,942		$ 94,338	$ 291,645		$ 286,385
Rental Expenses: Residential		0		0	0		0
Rental Expenses: Total		$ 99,942		$ 94,338	$ 291,645		$ 286,385
Rental Expenses: % Of Grand Totals		34.43%		35.98%	34.49%		37.08%
Net Operating Income		$ 160,984		$ 163,318	$ 480,415		$ 473,617
Net Operating Income: % of Grand Totals		32.93%		35.60%	33.31%		34.93%
Company's Share of Net Operating Income: % of Grand Totals		25.99%		29.06%	26.38%		28.35%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 134,938		$ 125,340	$ 401,020		$ 382,119
Rental Revenue: Residential	[1]	3,133		806	11,374		1,817
Rental Revenue Total	[1]	$ 138,071		$ 126,146	$ 412,394		$ 383,936
Rental Revenue: % of Grand Totals		17.72%		17.50%	18.02%		18.04%
Rental Expenses: Class A Office		$ 47,068		$ 43,582	$ 135,677		$ 124,785
Rental Expenses: Residential		2,125		1,688	9,138		4,918
Rental Expenses: Total		$ 49,193		$ 45,270	$ 144,815		$ 129,703
Rental Expenses: % Of Grand Totals		16.95%		17.26%	17.12%		16.79%
Net Operating Income		$ 88,878		$ 80,876	$ 267,579		$ 254,233
Net Operating Income: % of Grand Totals		18.18%		17.63%	18.55%		18.75%
Company's Share of Net Operating Income: % of Grand Totals		19.35%		19.39%	19.69%		20.50%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office		$ 12,293	[1]	$ 0	$ 18,765	[1]	$ 0
Rental Revenue: Residential		0	[1]	0	0	[1]	0
Rental Revenue Total		$ 12,293	[1]	$ 0	$ 18,765	[1]	$ 0
Rental Revenue: % of Grand Totals		1.58%		0.00%	0.82%		0.00%
Rental Expenses: Class A Office		$ 3,125		$ 0	$ 4,805		$ 0
Rental Expenses: Residential		0		0	0		0
Rental Expenses: Total		$ 3,125		$ 0	$ 4,805		$ 0
Rental Expenses: % Of Grand Totals		1.08%		0.00%	0.57%		0.00%
Net Operating Income		$ 9,168		$ 0	$ 13,960		$ 0
Net Operating Income: % of Grand Totals		1.88%		0.00%	0.97%		0.00%
Company's Share of Net Operating Income: % of Grand Totals		2.34%		0.15%	1.41%		0.05%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 88,954		$ 85,797	$ 280,473		$ 252,822
Rental Revenue: Residential	[1]	7,370		6,670	21,663		18,421
Rental Revenue Total	[1]	$ 96,324		$ 92,467	$ 302,136		$ 271,243
Rental Revenue: % of Grand Totals		12.36%		12.83%	13.21%		12.75%
Rental Expenses: Class A Office		$ 33,317		$ 31,619	$ 101,623		$ 94,360
Rental Expenses: Residential		3,347		2,961	9,655		8,896
Rental Expenses: Total		$ 36,664		$ 34,580	$ 111,278		$ 103,256
Rental Expenses: % Of Grand Totals		12.63%		13.19%	13.16%		13.37%
Net Operating Income		$ 59,660		$ 57,887	$ 190,858		$ 167,987
Net Operating Income: % of Grand Totals		12.20%		12.62%	13.23%		12.39%
Company's Share of Net Operating Income: % of Grand Totals		14.44%		14.32%	15.49%		14.24%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	$ 11,749		$ 5,189	$ 28,395		$ 7,382
Operating expense		8,548		3,946	19,832		7,993
Hotel [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	11,749		5,189	28,395		7,382
Operating expense		8,548		3,946	19,832		7,993
Hotel [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0		0	0		0
Operating expense		0		0	0		0
Hotel [Member] | New York [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0		0	0		0
Operating expense		0		0	0		0
Hotel [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0		0	0		0
Operating expense		0		0	0		0
Hotel [Member] | Seattle
Segment Reporting Information [Line Items]
Other revenue		0	[1]	0	0	[1]	0
Operating expense		0		0	0		0
Hotel [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	0		0	0		0
Operating expense		0		0	0		0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(48,306)		(47,800)	(143,223)		(138,463)
Noncontrolling interest - property partnerships [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(11,293)		(10,841)	(34,405)		(31,641)
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		(37,013)		(36,959)	(108,818)		(106,822)
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		8,169		3,464	25,996		9,369
Unconsolidated Joint Ventures [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		13,143		12,078	40,147		38,535
Unconsolidated Joint Ventures [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(259)		104	(397)		(517)
Unconsolidated Joint Ventures [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		3,233		3,502	9,597		10,562
Unconsolidated Joint Ventures [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		1,978		671	5,877		671
Unconsolidated Joint Ventures [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		9,052		4,447	27,127		15,858
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income		475,918		435,195	1,407,390		1,291,860
Company's Share [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		167,094		149,271	481,045		437,736
Company's Share [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		13,143		12,078	40,147		38,535
Company's Share [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		123,712		126,463	371,200		366,278
Company's Share [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		92,111		84,378	277,176		264,795
Company's Share [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		11,146		671	19,837		671
Company's Share [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		$ 68,712		$ 62,334	$ 217,985		$ 183,845

[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.