Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 832,365	$ 821,609	$ 2,489,563	$ 2,442,675
Rental Revenue: Residential	12,845	12,117	37,725	37,027
Rental Revenue Total	$ 858,372	$ 848,808	$ 2,564,820	$ 2,517,782
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%	100.00%
Rental Expenses: Office	$ 325,641	$ 321,909	$ 976,806	$ 946,067
Rental Expenses: Residential	6,095	5,988	18,570	17,413
Rental Expenses: Total	$ 341,364	$ 337,730	$ 1,021,934	$ 989,167
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%	100.00%
Net Operating Income	$ 517,008	$ 511,078	$ 1,542,886	$ 1,528,615
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: Office	$ 302,589	$ 300,613	$ 911,700	$ 866,431
Rental Revenue: Residential	4,633	4,219	13,162	12,687
Rental Revenue Total	$ 320,384	$ 319,914	$ 962,394	$ 917,198
Rental Revenue: % of Grand Totals	37.32%	37.69%	37.52%	36.42%
Rental Expenses: Office	$ 113,087	$ 107,876	$ 341,207	$ 321,955
Rental Expenses: Residential	1,943	1,621	5,424	4,757
Rental Expenses: Total	$ 124,658	$ 119,330	$ 373,189	$ 352,399
Rental Expenses: % Of Grand Totals	36.52%	35.34%	36.52%	35.62%
Net Operating Income	$ 195,726	$ 200,584	$ 589,205	$ 564,799
Net Operating Income: % of Grand Totals	37.85%	39.25%	38.19%	36.96%
Company's Share of Net Operating Income: % of Grand Totals	37.89%	39.89%	38.26%	37.51%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 17,735	$ 18,661	$ 52,516	$ 57,534
Rental Revenue: Residential	0	0	0	0
Rental Revenue Total	$ 17,735	$ 18,661	$ 52,516	$ 57,534
Rental Revenue: % of Grand Totals	2.07%	2.20%	2.05%	2.29%
Rental Expenses: Office	$ 1,613	$ 7,344	$ 15,059	$ 20,678
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Total	$ 1,613	$ 7,344	$ 15,059	$ 20,678
Rental Expenses: % Of Grand Totals	0.47%	2.17%	1.47%	2.09%
Net Operating Income	$ 16,122	$ 11,317	$ 37,457	$ 36,856
Net Operating Income: % of Grand Totals	3.12%	2.21%	2.43%	2.41%
Company's Share of Net Operating Income: % of Grand Totals	4.64%	3.64%	3.96%	3.89%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 263,212	$ 258,295	$ 790,726	$ 780,909
Rental Revenue: Residential	0	0	0	0
Rental Revenue Total	$ 263,212	$ 258,295	$ 790,726	$ 780,909
Rental Revenue: % of Grand Totals	30.66%	30.43%	30.83%	31.02%
Rental Expenses: Office	$ 113,951	$ 111,419	$ 338,588	$ 327,376
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Total	$ 113,951	$ 111,419	$ 338,588	$ 327,376
Rental Expenses: % Of Grand Totals	33.38%	32.99%	33.13%	33.10%
Net Operating Income	$ 149,261	$ 146,876	$ 452,138	$ 453,533
Net Operating Income: % of Grand Totals	28.87%	28.74%	29.30%	29.67%
Company's Share of Net Operating Income: % of Grand Totals	23.33%	23.41%	23.81%	24.21%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 127,441	$ 128,929	$ 378,629	$ 393,252
Rental Revenue: Residential	3,316	3,152	10,174	10,428
Rental Revenue Total	$ 130,757	$ 132,081	$ 388,803	$ 403,680
Rental Revenue: % of Grand Totals	15.23%	15.56%	15.16%	16.03%
Rental Expenses: Office	$ 53,077	$ 52,410	$ 151,261	$ 148,020
Rental Expenses: Residential	1,982	2,346	6,926	6,733
Rental Expenses: Total	$ 55,059	$ 54,756	$ 158,187	$ 154,753
Rental Expenses: % Of Grand Totals	16.13%	16.21%	15.48%	15.64%
Net Operating Income	$ 75,698	$ 77,325	$ 230,616	$ 248,927
Net Operating Income: % of Grand Totals	14.64%	15.13%	14.95%	16.28%
Company's Share of Net Operating Income: % of Grand Totals	16.09%	16.37%	16.41%	17.65%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 14,394	$ 10,821	$ 38,497	$ 32,251
Rental Revenue: Residential	0	0	0	0
Rental Revenue Total	$ 14,394	$ 10,821	$ 38,497	$ 32,251
Rental Revenue: % of Grand Totals	1.68%	1.27%	1.50%	1.28%
Rental Expenses: Office	$ 3,304	$ 3,382	$ 9,286	$ 9,753
Rental Expenses: Residential	0	0	0	0
Rental Expenses: Total	$ 3,304	$ 3,382	$ 9,286	$ 9,753
Rental Expenses: % Of Grand Totals	0.97%	1.00%	0.91%	0.99%
Net Operating Income	$ 11,090	$ 7,439	$ 29,211	$ 22,498
Net Operating Income: % of Grand Totals	2.15%	1.46%	1.89%	1.47%
Company's Share of Net Operating Income: % of Grand Totals	2.75%	1.87%	2.44%	1.89%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 106,994	$ 104,290	$ 317,495	$ 312,298
Rental Revenue: Residential	4,896	4,746	14,389	13,912
Rental Revenue Total	$ 111,890	$ 109,036	$ 331,884	$ 326,210
Rental Revenue: % of Grand Totals	13.04%	12.85%	12.94%	12.96%
Rental Expenses: Office	$ 40,609	$ 39,478	$ 121,405	$ 118,285
Rental Expenses: Residential	2,170	2,021	6,220	5,923
Rental Expenses: Total	$ 42,779	$ 41,499	$ 127,625	$ 124,208
Rental Expenses: % Of Grand Totals	12.53%	12.29%	12.49%	12.56%
Net Operating Income	$ 69,111	$ 67,537	$ 204,259	$ 202,002
Net Operating Income: % of Grand Totals	13.37%	13.21%	13.24%	13.21%
Company's Share of Net Operating Income: % of Grand Totals	15.30%	14.82%	15.12%	14.85%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	$ 13,162	$ 15,082	$ 37,532	$ 38,080
Operating expense	9,628	9,833	26,558	25,687
Hotel [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	13,162	15,082	37,532	38,080
Operating expense	9,628	9,833	26,558	25,687
Hotel [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0	0
Operating expense	0	0	0	0
Hotel [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0	0
Operating expense	0	0	0	0
Hotel [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0	0
Operating expense	0	0	0	0
Hotel [Member] \| Seattle
Segment Reporting Information [Line Items]
Other revenue	0	0	0	0
Operating expense	0	0	0	0
Hotel [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0	0
Operating expense	0	0	0	0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(51,504)	(44,487)	(152,768)	(138,448)
Noncontrolling interest - property partnerships [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(16,574)	(10,823)	(47,603)	(32,803)
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	(34,930)	(33,664)	(105,165)	(105,645)
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]
Segment Reporting Information [Line Items]
Net Operating Income	30,675	31,919	94,386	98,936
Unconsolidated Joint Ventures [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	8,903	9,099	26,424	26,547
Unconsolidated Joint Ventures [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	6,876	6,835	21,281	21,118
Unconsolidated Joint Ventures [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	1,423	3,472	6,447	12,614
Unconsolidated Joint Ventures [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	4,146	4,285	12,925	13,850
Unconsolidated Joint Ventures [Member] \| Seattle
Segment Reporting Information [Line Items]
Net Operating Income	2,545	1,899	7,079	5,713
Unconsolidated Joint Ventures [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	6,782	6,329	20,230	19,094
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income	496,179	498,510	1,484,504	1,489,103
Company's Share [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	188,055	198,860	568,026	558,543
Company's Share [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	22,998	18,152	58,738	57,974
Company's Share [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	115,754	116,684	353,420	360,502
Company's Share [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	79,844	81,610	243,541	262,777
Company's Share [Member] \| Seattle
Segment Reporting Information [Line Items]
Net Operating Income	13,635	9,338	36,290	28,211
Company's Share [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	$ 75,893	$ 73,866	$ 224,489	$ 221,096