v2.4.0.8
Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Segment Reporting Information [Line Items]        
Rental Revenue: Class A Office $ 475,965 $ 436,758 $ 926,527 $ 851,266
Rental Revenue: Office/Technical 14,896 9,942 24,743 19,685
Rental Revenue: Residential 5,484 5,036 11,062 9,517
Rental Revenue: Hotel 11,118 10,049 19,409 16,865
Total revenue 507,463 461,785 981,741 897,333
Rental Revenue: % of Grand Totals 100.00% 100.00% 100.00% 100.00%
Rental Expenses: Class A Office 173,237 155,944 340,298 306,500
Rental Expenses: Office/Technical 3,770 2,654 6,596 5,225
Rental Expenses: Residential 2,830 2,574 5,563 5,289
Rental Expenses: Hotel 7,335 6,616 14,379 12,715
Rental Expenses: Total 187,172 167,788 366,836 329,729
Rental Expenses: % Of Grand Totals 100.00% 100.00% 100.00% 100.00%
Net operating Income 320,291 293,997 614,905 567,604
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 164,855 157,642 326,358 298,650
Rental Revenue: Office/Technical 5,538 5,744 11,191 11,343
Rental Revenue: Residential 1,065 1,013 2,132 1,896
Rental Revenue: Hotel 11,118 10,049 19,409 16,865
Total revenue 182,576 174,448 359,090 328,754
Rental Revenue: % of Grand Totals 35.98% 37.78% 36.58% 36.64%
Rental Expenses: Class A Office 63,181 60,504 128,913 118,337
Rental Expenses: Office/Technical 1,627 1,652 3,414 3,152
Rental Expenses: Residential 407 367 850 757
Rental Expenses: Hotel 7,335 6,616 14,379 12,715
Rental Expenses: Total 72,550 69,139 147,556 134,961
Rental Expenses: % Of Grand Totals 38.76% 41.21% 40.22% 40.93%
Net operating Income 110,026 105,309 211,534 193,793
Net operating Income: % of Grand Totals 34.35% 35.82% 34.40% 34.14%
New York [Member]
        
Segment Reporting Information [Line Items]        
Rental Revenue: Class A Office 143,305 122,657 265,401 240,246
Rental Revenue: Office/Technical 0 0 0 0
Rental Revenue: Residential 0 0 0 0
Rental Revenue: Hotel 0 0 0 0
Total revenue 143,305 122,657 265,401 240,246
Rental Revenue: % of Grand Totals 28.24% 26.56% 27.03% 26.77%
Rental Expenses: Class A Office 48,205 38,936 90,092 77,443
Rental Expenses: Office/Technical 0 0 0 0
Rental Expenses: Residential 0 0 0 0
Rental Expenses: Hotel 0 0 0 0
Rental Expenses: Total 48,205 38,936 90,092 77,443
Rental Expenses: % Of Grand Totals 25.75% 23.21% 24.56% 23.49%
Net operating Income 95,100 83,721 175,309 162,803
Net operating Income: % of Grand Totals 29.69% 28.48% 28.51% 28.68%
Princeton [Member]
        
Segment Reporting Information [Line Items]        
Rental Revenue: Class A Office 14,853 15,617 31,280 30,467
Rental Revenue: Office/Technical 0 0 0 0
Rental Revenue: Residential 0 0 0 0
Rental Revenue: Hotel 0 0 0 0
Total revenue 14,853 15,617 31,280 30,467
Rental Revenue: % of Grand Totals 2.93% 3.38% 3.19% 3.40%
Rental Expenses: Class A Office 7,667 7,691 15,314 15,049
Rental Expenses: Office/Technical 0 0 0 0
Rental Expenses: Residential 0 0 0 0
Rental Expenses: Hotel 0 0 0 0
Rental Expenses: Total 7,667 7,691 15,314 15,049
Rental Expenses: % Of Grand Totals 4.10% 4.58% 4.17% 4.56%
Net operating Income 7,186 7,926 15,966 15,418
Net operating Income: % of Grand Totals 2.24% 2.70% 2.60% 2.72%
San Francisco [Member]
        
Segment Reporting Information [Line Items]        
Rental Revenue: Class A Office 53,331 52,102 106,002 102,766
Rental Revenue: Office/Technical 5,327 144 5,478 196
Rental Revenue: Residential 0 0 0 0
Rental Revenue: Hotel 0 0 0 0
Total revenue 58,658 52,246 111,480 102,962
Rental Revenue: % of Grand Totals 11.56% 11.31% 11.35% 11.47%
Rental Expenses: Class A Office 21,264 20,507 41,136 39,924
Rental Expenses: Office/Technical 1,116 38 1,151 62
Rental Expenses: Residential 0 0 0 0
Rental Expenses: Hotel 0 0 0 0
Rental Expenses: Total 22,380 20,545 42,287 39,986
Rental Expenses: % Of Grand Totals 11.96% 12.24% 11.53% 12.13%
Net operating Income 36,278 31,701 69,193 62,976
Net operating Income: % of Grand Totals 11.33% 10.78% 11.25% 11.10%
Washington, DC [Member]
        
Segment Reporting Information [Line Items]        
Rental Revenue: Class A Office 99,621 88,740 197,486 179,137
Rental Revenue: Office/Technical 4,031 4,054 8,074 8,146
Rental Revenue: Residential 4,419 4,023 8,930 7,621
Rental Revenue: Hotel 0 0 0 0
Total revenue 108,071 96,817 214,490 194,904
Rental Revenue: % of Grand Totals 21.29% 20.97% 21.85% 21.72%
Rental Expenses: Class A Office 32,920 28,306 64,843 55,747
Rental Expenses: Office/Technical 1,027 964 2,031 2,011
Rental Expenses: Residential 2,423 2,207 4,713 4,532
Rental Expenses: Hotel 0 0 0 0
Rental Expenses: Total 36,370 31,477 71,587 62,290
Rental Expenses: % Of Grand Totals 19.43% 18.76% 19.52% 18.89%
Net operating Income $ 71,701 $ 65,340 $ 142,903 $ 132,614
Net operating Income: % of Grand Totals 22.39% 22.22% 23.24% 23.36%