Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 3,328,778	$ 3,262,439	$ 3,119,999
Rental Revenue: Residential	50,543	49,508	47,592
Rental Revenue Total	$ 3,429,317	$ 3,363,171	$ 3,214,948
Rental Revenue: % of Grand Totals	100.00%	100.00%	100.00%
Rental Expenses: Office	$ 1,308,881	$ 1,263,366	$ 1,160,697
Rental Expenses: Residential	26,188	23,472	23,250
Rental Expenses: Total	$ 1,370,668	$ 1,322,126	$ 1,216,172
Rental Expenses: % Of Grand Totals	100.00%	100.00%	100.00%
Net Operating Income	$ 2,058,649	$ 2,041,045	$ 1,998,776
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	$ 1,218,009	$ 1,159,460	$ 1,093,840
Rental Revenue: Residential	17,909	17,198	16,452
Rental Revenue Total	$ 1,285,914	$ 1,227,882	$ 1,157,649
Rental Revenue: % of Grand Totals	37.49%	36.51%	36.01%
Rental Expenses: Office	$ 455,880	$ 427,446	$ 393,339
Rental Expenses: Residential	8,910	6,495	6,378
Rental Expenses: Total	$ 500,389	$ 469,229	$ 431,942
Rental Expenses: % Of Grand Totals	36.52%	35.49%	35.51%
Net Operating Income	$ 785,525	$ 758,653	$ 725,707
Net Operating Income: % of Grand Totals	38.16%	37.18%	36.31%
Company's Share of Net Operating Income: % of Grand Totals	38.29%	37.67%	36.35%
Los Angeles [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 70,519	$ 75,353	$ 3,890
Rental Revenue: Residential	0	0	0
Rental Revenue Total	$ 70,519	$ 75,353	$ 3,890
Rental Revenue: % of Grand Totals	2.06%	2.24%	0.12%
Rental Expenses: Office	$ 22,108	$ 27,537	$ 1,431
Rental Expenses: Residential	0	0	0
Rental Expenses: Total	$ 22,108	$ 27,537	$ 1,431
Rental Expenses: % Of Grand Totals	1.61%	2.08%	0.12%
Net Operating Income	$ 48,411	$ 47,816	$ 2,459
Net Operating Income: % of Grand Totals	2.35%	2.35%	0.12%
Company's Share of Net Operating Income: % of Grand Totals	3.88%	3.79%	2.61%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 1,054,594	$ 1,042,460	$ 1,053,615
Rental Revenue: Residential	0	0	0
Rental Revenue Total	$ 1,054,594	$ 1,042,460	$ 1,053,615
Rental Revenue: % of Grand Totals	30.75%	31.00%	32.77%
Rental Expenses: Office	$ 453,192	$ 437,600	$ 415,831
Rental Expenses: Residential	0	0	0
Rental Expenses: Total	$ 453,192	$ 437,600	$ 415,831
Rental Expenses: % Of Grand Totals	33.06%	33.10%	34.19%
Net Operating Income	$ 601,402	$ 604,860	$ 637,784
Net Operating Income: % of Grand Totals	29.21%	29.63%	31.91%
Company's Share of Net Operating Income: % of Grand Totals	23.67%	24.21%	25.62%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 509,920	$ 522,463	$ 539,904
Rental Revenue: Residential	14,017	13,668	14,102
Rental Revenue Total	$ 523,937	$ 536,131	$ 554,006
Rental Revenue: % of Grand Totals	15.28%	15.94%	17.23%
Rental Expenses: Office	$ 203,565	$ 199,324	$ 194,205
Rental Expenses: Residential	9,060	8,940	9,255
Rental Expenses: Total	$ 212,625	$ 208,264	$ 203,460
Rental Expenses: % Of Grand Totals	15.51%	15.75%	16.73%
Net Operating Income	$ 311,312	$ 327,867	$ 350,546
Net Operating Income: % of Grand Totals	15.12%	16.06%	17.54%
Company's Share of Net Operating Income: % of Grand Totals	16.58%	17.45%	18.66%
Seattle
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 49,269	$ 44,080	$ 63,830
Rental Revenue: Residential	0	0	0
Rental Revenue Total	$ 49,269	$ 44,080	$ 63,830
Rental Revenue: % of Grand Totals	1.44%	1.31%	1.99%
Rental Expenses: Office	$ 12,491	$ 13,170	$ 12,387
Rental Expenses: Residential	0	0	0
Rental Expenses: Total	$ 12,491	$ 13,170	$ 12,387
Rental Expenses: % Of Grand Totals	0.91%	1.00%	1.02%
Net Operating Income	$ 36,778	$ 30,910	$ 51,443
Net Operating Income: % of Grand Totals	1.79%	1.51%	2.57%
Company's Share of Net Operating Income: % of Grand Totals	2.32%	1.95%	3.00%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Office	$ 426,467	$ 418,623	$ 364,920
Rental Revenue: Residential	18,617	18,642	17,038
Rental Revenue Total	$ 445,084	$ 437,265	$ 381,958
Rental Revenue: % of Grand Totals	12.98%	13.00%	11.88%
Rental Expenses: Office	$ 161,645	$ 158,289	$ 143,504
Rental Expenses: Residential	8,218	8,037	7,617
Rental Expenses: Total	$ 169,863	$ 166,326	$ 151,121
Rental Expenses: % Of Grand Totals	12.39%	12.58%	12.43%
Net Operating Income	$ 275,221	$ 270,939	$ 230,837
Net Operating Income: % of Grand Totals	13.37%	13.27%	11.55%
Company's Share of Net Operating Income: % of Grand Totals	15.26%	14.93%	13.76%
Hotel [Member]
Segment Reporting Information [Line Items]
Other revenue	$ 49,996	$ 51,224	$ 47,357
Operating expense	35,599	35,288	32,225
Hotel [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Other revenue	49,996	51,224	47,357
Operating expense	35,599	35,288	32,225
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]
Net Operating Income	(204,433)	(186,707)	(194,365)
Noncontrolling interest - property partnerships [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(64,069)	(46,487)	(45,730)
Noncontrolling interest - property partnerships [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0
Noncontrolling interest - property partnerships [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	(140,364)	(140,220)	(148,635)
Noncontrolling interest - property partnerships [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0
Noncontrolling interest - property partnerships [Member] \| Seattle
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0
Noncontrolling interest - property partnerships [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0
Unconsolidated Joint Ventures [Member]
Segment Reporting Information [Line Items]
Net Operating Income	122,569	129,718	160,695
Unconsolidated Joint Ventures [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	35,274	35,298	34,376
Unconsolidated Joint Ventures [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	28,381	27,367	48,818
Unconsolidated Joint Ventures [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	6,853	15,612	14,314
Unconsolidated Joint Ventures [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	16,537	18,312	16,203
Unconsolidated Joint Ventures [Member] \| Seattle
Segment Reporting Information [Line Items]
Net Operating Income	9,023	7,788	7,494
Unconsolidated Joint Ventures [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	26,501	25,341	39,490
Company's Share [Member]
Segment Reporting Information [Line Items]
Net Operating Income	1,976,785	1,984,056	1,965,106
Company's Share [Member] \| Boston [Member]
Segment Reporting Information [Line Items]
Net Operating Income	756,730	747,464	714,353
Company's Share [Member] \| Los Angeles [Member]
Segment Reporting Information [Line Items]
Net Operating Income	76,792	75,183	51,277
Company's Share [Member] \| New York [Member]
Segment Reporting Information [Line Items]
Net Operating Income	467,891	480,252	503,463
Company's Share [Member] \| San Francisco [Member]
Segment Reporting Information [Line Items]
Net Operating Income	327,849	346,179	366,749
Company's Share [Member] \| Seattle
Segment Reporting Information [Line Items]
Net Operating Income	45,801	38,698	58,937
Company's Share [Member] \| Washington, DC [Member]
Segment Reporting Information [Line Items]
Net Operating Income	$ 301,722	$ 296,280	$ 270,327