Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 3,262,439	$ 3,119,999	$ 2,968,412
Rental Revenue: Residential	49,508	47,592	57,181
Rental Revenue Total	$ 3,363,171	$ 3,214,948	$ 3,065,075
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%
Rental Expenses: Office	$ 1,263,366	$ 1,160,697	$ 1,078,487
Rental Expenses: Residential	23,472	23,250	29,583
Rental Expenses: Total	$ 1,322,126	$ 1,216,172	$ 1,135,548
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%
Company's share of net operating income from joint ventures	$ 2,041,045	$ 1,998,776	$ 1,929,527
Net Operating Income: % of Grand Totals	100.00%	100.00%	100.00%
Company's Share of Net Operating Income: % of Grand Totals	100.00%	100.00%	100.00%
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 1,159,460	$ 1,093,840	$ 1,005,156
Rental Revenue: Residential	17,198	16,452	15,086
Rental Revenue Total	$ 1,227,882	$ 1,157,649	$ 1,059,724
Rental Revenue: % of Grand Totals	36.51%	36.01%	34.58%
Rental Expenses: Office	$ 427,446	$ 393,339	$ 360,218
Rental Expenses: Residential	6,495	6,378	5,961
Rental Expenses: Total	$ 469,229	$ 431,942	$ 393,657
Rental Expenses: % Of Grand Totals	35.49%	35.51%	34.66%
Company's share of net operating income from joint ventures	$ 758,653	$ 725,707	$ 666,067
Net Operating Income: % of Grand Totals	37.18%	36.31%	34.52%
Company's Share of Net Operating Income: % of Grand Totals	37.67%	36.35%	34.75%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 75,353	$ 3,890	$ 0
Rental Revenue: Residential	0	0	0
Rental Revenue Total	$ 75,353	$ 3,890	$ 0
Rental Revenue: % of Grand Totals	2.24%	0.12%	0.00%
Rental Expenses: Office	$ 27,537	$ 1,431	$ 0
Rental Expenses: Residential	0	0	0
Rental Expenses: Total	$ 27,537	$ 1,431	$ 0
Rental Expenses: % Of Grand Totals	2.08%	0.12%	0.00%
Company's share of net operating income from joint ventures	$ 47,816	$ 2,459	$ 0
Net Operating Income: % of Grand Totals	2.35%	0.12%	0.00%
Company's Share of Net Operating Income: % of Grand Totals	3.79%	2.61%	2.81%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 1,042,460	$ 1,053,615	$ 1,031,479
Rental Revenue: Residential	0	0	0
Rental Revenue Total	$ 1,042,460	$ 1,053,615	$ 1,031,479
Rental Revenue: % of Grand Totals	31.00%	32.77%	33.65%
Rental Expenses: Office	$ 437,600	$ 415,831	$ 391,293
Rental Expenses: Residential	0	0	0
Rental Expenses: Total	$ 437,600	$ 415,831	$ 391,293
Rental Expenses: % Of Grand Totals	33.10%	34.19%	34.46%
Company's share of net operating income from joint ventures	$ 604,860	$ 637,784	$ 640,186
Net Operating Income: % of Grand Totals	29.63%	31.91%	33.18%
Company's Share of Net Operating Income: % of Grand Totals	24.21%	25.62%	26.32%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 522,463	$ 539,904	$ 534,397
Rental Revenue: Residential	13,668	14,102	14,769
Rental Revenue Total	$ 536,131	$ 554,006	$ 549,166
Rental Revenue: % of Grand Totals	15.94%	17.23%	17.92%
Rental Expenses: Office	$ 199,324	$ 194,205	$ 183,353
Rental Expenses: Residential	8,940	9,255	11,371
Rental Expenses: Total	$ 208,264	$ 203,460	$ 194,724
Rental Expenses: % Of Grand Totals	15.75%	16.73%	17.15%
Company's share of net operating income from joint ventures	$ 327,867	$ 350,546	$ 354,442
Net Operating Income: % of Grand Totals	16.06%	17.54%	18.37%
Company's Share of Net Operating Income: % of Grand Totals	17.45%	18.66%	19.49%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 44,080	$ 63,830	$ 31,978
Rental Revenue: Residential	0	0	0
Rental Revenue Total	$ 44,080	$ 63,830	$ 31,978
Rental Revenue: % of Grand Totals	1.31%	1.99%	1.04%
Rental Expenses: Office	$ 13,170	$ 12,387	$ 8,386
Rental Expenses: Residential	0	0	0
Rental Expenses: Total	$ 13,170	$ 12,387	$ 8,386
Rental Expenses: % Of Grand Totals	1.00%	1.02%	0.74%
Company's share of net operating income from joint ventures	$ 30,910	$ 51,443	$ 23,592
Net Operating Income: % of Grand Totals	1.51%	2.57%	1.22%
Company's Share of Net Operating Income: % of Grand Totals	1.95%	3.00%	1.66%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 418,623	$ 364,920	$ 365,402
Rental Revenue: Residential	18,642	17,038	27,326
Rental Revenue Total	$ 437,265	$ 381,958	$ 392,728
Rental Revenue: % of Grand Totals	13.00%	11.88%	12.81%
Rental Expenses: Office	$ 158,289	$ 143,504	$ 135,237
Rental Expenses: Residential	8,037	7,617	12,251
Rental Expenses: Total	$ 166,326	$ 151,121	$ 147,488
Rental Expenses: % Of Grand Totals	12.58%	12.43%	12.99%
Company's share of net operating income from joint ventures	$ 270,939	$ 230,837	$ 245,240
Net Operating Income: % of Grand Totals	13.27%	11.55%	12.71%
Company's Share of Net Operating Income: % of Grand Totals	14.93%	13.76%	14.97%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	$ 51,224	$ 47,357	$ 39,482
Operating expense	35,288	32,225	27,478
Hotel [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	51,224	47,357	39,482
Operating expense	35,288	32,225	27,478
Hotel [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0
Operating expense	0	0	0
Hotel [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0
Operating expense	0	0	0
Hotel [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0
Operating expense	0	0	0
Hotel [Member] \| Seattle
Segment Reporting Information [Line Items]
Other revenue	0	0	0
Operating expense	0	0	0
Hotel [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Other revenue	0	0	0
Operating expense	0	0	0
Noncontrolling interest - property partnerships [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	(186,707)	(194,365)	(191,812)
Noncontrolling interest - property partnerships [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	(46,487)	(45,730)	(45,822)
Noncontrolling interest - property partnerships [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	0	0	0
Noncontrolling interest - property partnerships [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	(140,220)	(148,635)	(145,990)
Noncontrolling interest - property partnerships [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	0	0	0
Noncontrolling interest - property partnerships [Member] \| Seattle
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	0	0	0
Noncontrolling interest - property partnerships [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	0	0	0
Unconsolidated Joint Ventures [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	129,718	160,695	146,081
Unconsolidated Joint Ventures [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	35,298	34,376	34,233
Unconsolidated Joint Ventures [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	27,367	48,818	53,023
Unconsolidated Joint Ventures [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	15,612	14,314	1,594
Unconsolidated Joint Ventures [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	18,312	16,203	12,785
Unconsolidated Joint Ventures [Member] \| Seattle
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	7,788	7,494	7,690
Unconsolidated Joint Ventures [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	25,341	39,490	36,756
Company's Share [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	1,984,056	1,965,106	1,883,796
Company's Share [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	747,464	714,353	654,478
Company's Share [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	75,183	51,277	53,023
Company's Share [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	480,252	503,463	495,790
Company's Share [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	346,179	366,749	367,227
Company's Share [Member] \| Seattle
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	38,698	58,937	31,282
Company's Share [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Company's share of net operating income from joint ventures	$ 296,280	$ 270,327	$ 281,996