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Investment in unconsolidated Joint Ventures (Narrative) (Details) (USD $)
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3 Months Ended | 6 Months Ended | 0 Months Ended | 0 Months Ended | 0 Months Ended | 0 Months Ended | 6 Months Ended | 0 Months Ended | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Jun. 30, 2013
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Jun. 30, 2012
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Jun. 30, 2013
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Jun. 30, 2012
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May 30, 2013
125 West 55th Street [Member]
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Apr. 10, 2013
125 West 55th Street [Member]
sqft
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Feb. 28, 2013
Annapolis Junction Building Six [Member]
sqft
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May 31, 2013
500 North Capitol [Member]
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Jun. 30, 2013
500 North Capitol [Member]
sqft
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Apr. 04, 2013
Annapolis Junction Building Seven [Member]
Y
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Apr. 10, 2013
Mountain View Research [Member]
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Apr. 10, 2013
Mountain View Technology [Member]
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Apr. 10, 2013
Mountain View Research And Technology Parks [Member]
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Jun. 05, 2013
540 Madison Avenue [Member]
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Apr. 10, 2013
Company [Member]
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May 30, 2013
Company [Member]
125 West 55th Street [Member]
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Apr. 10, 2013
Mountain View Research And Technology Parks [Member]
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May 31, 2013
767 Fifth Avenue (The GM Building) [Member]
partners
sqft
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Jun. 30, 2012
767 Fifth Avenue (The GM Building) [Member]
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Apr. 10, 2013
Mountain View Technology [Member]
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Apr. 10, 2013
Mountain View Research [Member]
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May 31, 2013
Construction Loans [Member]
500 North Capitol [Member]
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May 31, 2013
Construction Loans [Member]
Company [Member]
500 North Capitol [Member]
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May 31, 2013
First Mortgage [Member]
500 North Capitol [Member]
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Jun. 05, 2013
First Mortgage [Member]
540 Madison Avenue [Member]
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Jun. 05, 2013
Prior to refinance first mortgage loan [Member]
540 Madison Avenue [Member]
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Jun. 05, 2013
Prior to refinance first mortgage loan [Member]
Company [Member]
540 Madison Avenue [Member]
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| Schedule of Equity Method Investments [Line Items] | |||||||||||||||||||||||||||
| Number of Joint Venture Partners | 2 | ||||||||||||||||||||||||||
| Contractual Sales Price | $ 470,000,000 | ||||||||||||||||||||||||||
| Carrying Value of Debt Assumed in Sale | 198,600,000 | ||||||||||||||||||||||||||
| Repayments of Notes Payable | 3,700,000 | 8,600,000 | |||||||||||||||||||||||||
| Debt Instrument, Basis Spread on Variable Rate | 1.65% | 2.00% | 2.50% | 1.65% | 1.50% | ||||||||||||||||||||||
| Maturity date | Mar. 10, 2020 | Apr. 04, 2016 | May 31, 2014 | Nov. 22, 2014 | Oct. 14, 2014 | Jun. 06, 2023 | Jun. 05, 2018 | Jul. 11, 2013 | |||||||||||||||||||
| Proceeds from Sale of Equity Method Investments | 201,182,000 | 3,057,000 | 253,700,000 | 152,200,000 | |||||||||||||||||||||||
| Losses from early extinguishment of debt | (152,000) | (274,000) | (152,000) | (1,041,000) | 400,000 | 200,000 | 1,000,000 | 300,000 | 300,000 | 200,000 | |||||||||||||||||
| Proceeds from Issuance of Secured Debt | 105,000,000 | 120,000,000 | |||||||||||||||||||||||||
| Coupon/Stated Rate | 6.09% | 4.15% | 5.20% | ||||||||||||||||||||||||
| Debt Instrument, Description of Variable Rate Basis | LIBOR plus 1.65% | LIBOR plus 2.00% | LIBOR plus 2.50% | LIBOR plus 1.50% | |||||||||||||||||||||||
| Equity Method Investment, Ownership Percentage | 60.00% | 50.00% | 30.00% | 30.00% | 50.00% | 60.00% | |||||||||||||||||||||
| Ownerhip upon acquistion | 100.00% | ||||||||||||||||||||||||||
| Gain on consolidation of joint ventures | 387,801,000 | 0 | 387,801,000 | 0 | 24,400,000 | 363,400,000 | 363,400,000 | ||||||||||||||||||||
| Construction Loan Facility Borrowing Capacity | 22,000,000 | ||||||||||||||||||||||||||
| Net Rentable Area | 588,000 | 119,000 | 231,000 | 1,800,000 | |||||||||||||||||||||||
| Gain on sale or real estate | 43,300,000 | ||||||||||||||||||||||||||
| Number of extensions | 2 | ||||||||||||||||||||||||||
| Repayments of Secured Debt | $ 79,865,000 | $ 219,865,000 | $ 20,000,000 | $ 90,000,000 | $ 90,600,000 | $ 118,000,000 | |||||||||||||||||||||
| Extension Option (in years) | 1 | ||||||||||||||||||||||||||