v2.4.0.8

Real Estate Activity During the Six Months Ended June 30, 2013 (Narrative) (Details) (USD $) | 3 Months Ended | 6 Months Ended | 0 Months Ended |  |  |  | 0 Months Ended | 3 Months Ended |  | 0 Months Ended | 6 Months Ended | 3 Months Ended |  | 3 Months Ended |  | 0 Months Ended | 1 Months Ended
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Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012 | Feb. 06, 2013 535 Mission [Member] floor sqft | Mar. 22, 2013 Two Patriots Park [Member] sqft | Apr. 25, 2013 Siz Zero One Massachusetts Avenue [Member] sqft | Jun. 14, 2013 Seventeen Cambridge Center [Member] sqft | Mar. 26, 2013 Transbay Tower [Member] floor sqft | Feb. 26, 2013 Transbay Tower [Member] | Feb. 07, 2013 Transbay Tower [Member] | Mar. 29, 2013 Reston Land Parcel [Member] sqft | Mar. 31, 2013 Plaza at Almaden [Member] | Mar. 28, 2013 Plaza at Almaden [Member] sqft | Feb. 20, 2013 Montvale Center [Member] | Jun. 30, 2012 Montvale Center [Member] | Jun. 30, 2013 303 Almaden Blvd [Member] | Mar. 31, 2013 303 Almaden Blvd [Member] | Mar. 28, 2013 303 Almaden Blvd [Member] sqft | Jun. 30, 2013 Mountain View Research And Technology Parks [Member] | Apr. 10, 2013 Mountain View Research And Technology Parks [Member] | Apr. 10, 2013 Mountain View Research [Member] Buildings sqft | Apr. 10, 2013 Mountain View Technology [Member] Buildings sqft | May 31, 2013 767 Fifth Avenue (The GM Building) [Member] partners sqft | Jun. 30, 2013 767 Fifth Avenue (The GM Building) [Member]
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 515,320,000 | $ 471,349,000 | $ 998,334,000 | $ 915,042,000 |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,529,000 |  |  | $ 5,200,000 |  |  |  |  | $ 22,600,000
Operating income | 170,815,000 | 173,319,000 | 301,250,000 | 316,886,000 |  |  |  |  |  |  |  |  |  |  |  |  | 873,000 |  |  | (300,000) |  |  |  |  | 400,000
Number of Joint Venture Partners |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |
Purchase price |  |  | 522,900,000 | 621,359,000 | 71,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of floors real estate |  |  |  |  | 27 |  |  |  | 60 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of debt extinguished |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,000,000 |  |  |  |  |  |  |  |  |
Gain on forgiveness of debt from discontinued operations | 0 | 0 | 20,182,000 | 0 |  |  |  |  |  |  |  |  |  |  | 20,200,000 | 17,800,000 | 0 |  |  |  |  |  |  |  |
Net Rentable Area |  |  |  |  | 307,000 | 256,000 | 478,000 | 195,000 | 1,400,000 |  |  | 250,000 |  | 840,000 |  |  |  |  | 158,000 |  |  | 604,000 | 135,000 | 1,800,000 |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 233,500,000 |  |  |  |
Impairment loss from discontinued operations | 0 | 0 | 3,241,000 | 0 |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 3,200,000 |  |  |  |  |  |  |
Ownership Percentage |  |  |  |  |  |  |  |  | 95.00% | 95.00% |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |
Payments to Acquire Land |  |  |  |  |  |  |  |  | 192,000,000 |  |  | 27,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Partners Joint Venture Ownership Percentage |  |  |  |  |  |  |  |  |  | 5.00% | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contractual Sales Price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40,000,000 |  |  |  |  |  |
Impairment loss | $ 0 | $ 0 | $ 8,306,000 | $ 0 |  |  |  |  |  |  |  |  | $ 8,300,000 |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate properties |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16 | 7 |  |

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