Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023		Mar. 31, 2022
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 769,158		$ 726,888
Rental Revenue: Residential	[1]	11,726		12,966
Rental Revenue Total	[1]	$ 788,985		$ 744,411
Rental Revenue: % of Grand Totals		100.00%		100.00%
Rental Expenses: Class A Office		$ 285,845		$ 263,823
Rental Expenses: Residential		5,463		6,432
Rental Expenses: Total		$ 297,979		$ 275,095
Rental Expenses: % Of Grand Totals		100.00%		100.00%
Net Operating Income		$ 491,006		$ 469,316
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]	$ 269,951		$ 242,078
Rental Revenue: Residential	[1]	4,049		3,596
Rental Revenue Total	[1]	$ 282,101		$ 250,231
Rental Revenue: % of Grand Totals		35.76%		33.61%
Rental Expenses: Class A Office		$ 100,049		$ 90,528
Rental Expenses: Residential		1,552		1,437
Rental Expenses: Total		$ 108,272		$ 96,805
Rental Expenses: % Of Grand Totals		36.34%		35.19%
Net Operating Income		$ 173,829		$ 153,426
Net Operating Income: % of Grand Totals		35.41%		32.69%
Company's Share of Net Operating Income: % of Grand Totals		35.41%		32.94%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 0		$ 0
Rental Revenue: Residential	[1]	0		0
Rental Revenue Total	[1]	$ 0		$ 0
Rental Revenue: % of Grand Totals		0.00%		0.00%
Rental Expenses: Class A Office		$ 0		$ 0
Rental Expenses: Residential		0		0
Rental Expenses: Total		$ 0		$ 0
Rental Expenses: % Of Grand Totals		0.00%		0.00%
Net Operating Income		$ 0		$ 0
Net Operating Income: % of Grand Totals		0.00%		0.00%
Company's Share of Net Operating Income: % of Grand Totals		2.73%		2.99%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 258,192		$ 256,870
Rental Revenue: Residential	[1]	0		0
Rental Revenue Total	[1]	$ 258,192		$ 256,870
Rental Revenue: % of Grand Totals		32.72%		34.51%
Rental Expenses: Class A Office		$ 102,485		$ 96,340
Rental Expenses: Residential		0		0
Rental Expenses: Total		$ 102,485		$ 96,340
Rental Expenses: % Of Grand Totals		34.39%		35.02%
Net Operating Income		$ 155,707		$ 160,530
Net Operating Income: % of Grand Totals		31.71%		34.21%
Company's Share of Net Operating Income: % of Grand Totals		25.39%		27.21%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 136,093		$ 132,375
Rental Revenue: Residential	[1]	3,642		2,391
Rental Revenue Total	[1]	$ 139,735		$ 134,766
Rental Revenue: % of Grand Totals		17.71%		18.10%
Rental Expenses: Class A Office		$ 46,085		$ 43,408
Rental Expenses: Residential		2,173		1,868
Rental Expenses: Total		$ 48,258		$ 45,276
Rental Expenses: % Of Grand Totals		16.20%		16.46%
Net Operating Income		$ 91,477		$ 89,490
Net Operating Income: % of Grand Totals		18.63%		19.07%
Company's Share of Net Operating Income: % of Grand Totals		19.59%		20.16%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office		$ 14,258	[1]	$ 0
Rental Revenue: Residential		0	[1]	0
Rental Revenue Total		$ 14,258	[1]	$ 0
Rental Revenue: % of Grand Totals		1.81%		0.00%
Rental Expenses: Class A Office		$ 2,960		$ 0
Rental Expenses: Residential		0		0
Rental Expenses: Total		$ 2,960		$ 0
Rental Expenses: % Of Grand Totals		0.99%		0.00%
Net Operating Income		$ 11,298		$ 0
Net Operating Income: % of Grand Totals		2.30%		0.00%
Company's Share of Net Operating Income: % of Grand Totals		2.71%		0.43%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	[1]	$ 90,664		$ 95,565
Rental Revenue: Residential	[1]	4,035		6,979
Rental Revenue Total	[1]	$ 94,699		$ 102,544
Rental Revenue: % of Grand Totals		12.00%		13.78%
Rental Expenses: Class A Office		$ 34,266		$ 33,547
Rental Expenses: Residential		1,738		3,127
Rental Expenses: Total		$ 36,004		$ 36,674
Rental Expenses: % Of Grand Totals		12.08%		13.33%
Net Operating Income		$ 58,695		$ 65,870
Net Operating Income: % of Grand Totals		11.95%		14.03%
Company's Share of Net Operating Income: % of Grand Totals		14.17%		16.27%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	$ 8,101		$ 4,557
Operating expense		6,671		4,840
Hotel [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	[1]	8,101		4,557
Operating expense		6,671		4,840
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		0	[1]	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		(47,097)		(47,055)
Noncontrolling interest - property partnerships [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		(10,817)		(11,735)
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		(36,280)		(35,320)
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] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		8,577		9,693
Unconsolidated Joint Ventures [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		13,225		13,757
Unconsolidated Joint Ventures [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		3,650		(156)
Unconsolidated Joint Ventures [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		3,464		3,181
Unconsolidated Joint Ventures [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		1,846		1,955
Unconsolidated Joint Ventures [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		9,994		8,891
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income		484,665		459,582
Company's Share [Member] | Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income		171,589		151,384
Company's Share [Member] | Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income		13,225		13,757
Company's Share [Member] | New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income		123,077		125,054
Company's Share [Member] | San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income		94,941		92,671
Company's Share [Member] | Seattle
Segment Reporting Information [Line Items]
Net Operating Income		13,144		1,955
Company's Share [Member] | Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income		$ 68,689		$ 74,761

[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.